Poppy needs to keep either her passive or her ult, otherwise, she's not Poppy.
I don't main Poppy, but I do really like her, and as someone who used to main Veigar, I'm here to tell you that Poppy's about to get Veigar'd.
I've just become aware that back in March, Meddler basically said that the upcoming Poppy rework would remove her passive and her ult, and only keep her E. Link, also, Solcrushed, who's working on her rework, if I'm not mistaken, has apparently said that her E is the most iconic part of her kit. Link, scroll down a bit. I don't agree with this at all, and I'm pretty sure most Poppy players don't either.
The most iconic parts of her kit are the parts that allow her to charge into the enemy team like the Juggernaut and get away with it, aka; her passive and her ult. It's her survivability that makes her iconic not the "charge-in" part. While everyone else on the team is busy playing long range League of Dodgeball, Poppy just says "fuck it, I'm going in" and if the Poppy player is good, they succeed. If they aren't good, or if they miscalculated, they get destroyed, just like anyone else who makes an ill-advised engage, and if you don't agree with this answer one question. If Poppy truly is unstoppable and always succeeds when diving, why isn't she on every team, why isn't she a perma-ban?
Here's the thing. Poppy is a very unpopular pick right now (and as far as I know, she pretty much always has been) and the reason for that is because there really isn't anything she does well enough to be picked for any other reason other than the way she "feels." She gets countered hard in lane very easily, possibly worse than any other champion. It's amazingly easy to deny her farm. Poppy is always going to have a difficult time surviving and farming early game. Her mana costs are so abysmal that she also has to make sure she picks her fights correctly too or she'll be left with no oomph and no ability to threaten her lane opponent. Some may argue that she's a virtually unstoppable high reward champion in late game, which is true, if the liability of being Poppy doesn't backfire to the point where she never reaches lategame which it often does. My point being, she may be high reward, but she is also deceptively high risk as well. It's a fair tradeoff.
Poppy right now has a unique feel among all 124 of the champions in League of Legends, she is literally the only champion who does what she does and feels the way she feels. If Riot simply turns her into a tank, as they seem to be indicating, then why would I pick Poppy over the 10 to 20 other champions who also fill that role? Obviously, based on the fact that she's 121st most picked out of 124 options "Why would I pick Poppy?" Is a question most League of Legends players are already asking. But I think I know the answer, at least for those of us who do pick her.
Why do we pick Poppy?
To me the "feeling" of Poppy is unique there are several aspects and attributes about Poppy that make her different from the other 123 champions in the game.
~ Revenge: Poppy spends most of the laning phase in most games getting destroyed. Denied farm at best, killed over and over at worst. (I can't speak to jungle Poppy, never really messed with that.) Her passive is literally the only thing that makes her laning phase possible. She can sit there at 10% health and the Poppy player can make a calculated risk to go in and Q the cannon minion, because they know they still have a chance to get that sweet, sweet 40 gold, and if they're lucky get out alive. The point I'm making though is that in most cases Poppy spends 10 to 15 minutes every game getting abused relentlessly and having a terrible time (unless the Poppy player is super skilled or their opponent is very unskilled, or your jungler camps top lane.)
Then, it happens. Poppy finally gets enough ranks in her Q, or gets her first full item (for me it's usually Triforce) and then it's like she just explodes. Poppy's finally done with your shit and now it's payback time. She's like George McFly knocking out Biff in Back to the Future. The kid who spent the whole game getting picked on, and now she's a certified badass and the other team needs to look out because it's time for some hammer diplomacy. As a Poppy player the moment when you get that shut-down on the top laner who's been harassing you the whole game is one of the best feels you can ever have playing League of Legends. Although the double and triple kills she gets in the ensuing teamfights because the enemy team has no idea that they need to be afraid of her are great feels too.
~Determination: This one really fits with her story and theme as well, just like Poppy in her story never gave up in the presence of crushing adversity, Poppy players know that if they hang in there long enough, and somehow make it to late game, anything is possible. Poppy is like the 2004 Red Sox, they haven't won in 86 years and they're down 0-3 to the Yankees in the pennant, but somehow determined enough to reverse-sweep and pull out the 4-3 win, then sweep the World Series. Again, a lot of this is due to her passive, but the decision making surrounding it is something that's actually present the whole game. Poppy constantly has to make decisions revolving around weather her passive will allow her to get what she's after, whether it's farm, or a surprise kill on the lane opponent. But this isn't without tons of risk. I don't know how many times I've dived my lane opponent as Poppy, stayed for the fight cause I knew if my Q came up again I'd get the kill despite the damage they're putting on to me, got the kill and then died to creeps because of course I had to fight them in their creep wave and those caster minion bolts aren't mitigated by my passive. Point is, I'm not very skilled, a good Poppy player knows when and more importantly how to never give up, and when that works, it just feels like such a Poppy thing to do. Poppy's ult contributes to this too. She's one of the few champions who can legitimately take a deep breath, and then hit the tower-dive button, and exhale if/when she gets out alive. It's always a tense moment and not as much of a "free win" as her opponents seem to think it is. Especially because good opponents should be able to anticipate and even bait it. Also I really feel that in the current state of "get baron and poke the tower down from long range" that seems to be the only way to take base turrets nowadays, having at least one champion who just goes in isn't unhealthy at all, especially if it's accompanied by the appropriate amount of risk.
~The Yolo Factor: To be fair, every champion has this. The button they press when they just want to start some shit. But most of them die when they do it, or they bank on their insane burst damage preventing them getting killed in return (Kat, Zed, Riven.) But Poppy's version is a little bit different, Poppy is uniquely able to get away with "just engaging" without having to fear getting bursted instantly like assassins do because of her ult and passive. Now I understand that typically this type of engage is reserved for assassins, and I understand that Poppy is sort of played like an assassin and that doesn't fit her. She shouldn't be an assassin, I agree with that, I think she should do a bit more sustained damage over time, because defensively she's strong enough to "just engage" and stay in the fight without relying on burst like she does now. I do think she needs a rework, but I also think she needs to keep her ability to engage and stay safe, but maybe lose a bit of her ability to assassinate as compensation. If she did a little less damage (or had to "spend" more to do the same damage [in the form of say, cooldowns because lord knows her mana costs are already insane]) but had the same capacity to survive, this is what she needs to keep her feel. My main point being, Poppy's identity is tied to her ability to engage and survive, not in the specific way she engages. Her E is a great part of her identity, her R is a better one. Right now all of her power budget is in her Q, and sort of her R, her W doesn't do anything (except keep her semi-relevant in league of mobility) and her E is only situationally useful. Poppy can survive without her ult, she could maybe survive without her passive (though I'm not too big on that prospect) but if she loses both, she's lost everything that makes her unique. (In fact I could even envision a world where Poppy's ult becomes her passive, but then I'd worry it would basically make her too similar to Alistar, especially since her E and his headbutt are virtually the same already and if this change were made their ults would be virtually the same too.) A successful Poppy rework will move her damage around (possibly nerf it a bit) and not just front-load all of it on her Q, fix her mana problems and make her laning a bit more tolerable, and keep her more or less just as safe when yoloing into the enemy team or turrets. This is a key part of her identity that's being thrown out the window I'm afraid. Now the obvious thing to say here is "well what if the rework does all this, but without her current passive and her current ult?" Well, if it did that'd be great, but I kind of don't know how it would without replacing them with abilities that are equally "unhealthy." Effectively the "problem" with Poppy now is that late game or super-fed Poppy can yolo, and get at least one guaranteed kill without fear of retribution. I feel like a slight nerf to her damage and/or her ult timer would fix this, without doing away with her ability to yolo-dive, or changing what her abilities do. (Too much of a nerf to her damage though would discourage diving and therefore make her "just another tank" so it's a fine line that's difficult to balance and still maintain her identity, but identity is the only think keeping her even remotely relevant right now.)
Finally, we play Poppy because:
~She's The Underdog: Big things come in small packages, and everyone loves the underdog. Anyone who's ever lost to Poppy, or ever won with her understands this completely. People argue Poppy's passive is bad because it has clarity issues aka; "as Poppy's opponent, I don't know if I can kill her based on her current health." It's easy to make the argument that this is "unhealthy" for the game, but I'd argue it's actually essential to Poppy's feel. And Poppy is not the only champion with deception built into her kit, other champions can be deceptive, Shaco and LeBlanc are the most blatant examples, but even some tanks like Volibear with his passive have similar deceptive qualities. Her passive is deceiving, yes, but this isn't a problem thematically, in fact it's no different from the way her size and appearance belie her true power (this is also why Lollipoppy is the best skin in the game, but I digress.) Poppy is the underdog from start to finish. 121st most popular pick out of 124 options, spends the early part of most games losing, has the worst mana management of anyone, but through determination, cunning, and a little bit of deception, she hides her true power until it's too late for her enemies to do anything about it. Poppy is a true hero, and League of Legends needs this kind of hero, the unpopular kind, the one who takes abuse but never quits, the kind that doesn't attract many followers, but who, nevertheless stands victorious in the end because the player who chose her believed, persevered, and crushed her naysayers under the surprising might of her hammer.
If Poppy loses her ult and her passive, what will she be? Just another tank who soaks damage and delays the enemy team until her team can show up and get the kills? Just another wet noodle fight in top lane until there's a teamfight at Dragon? League of Legends has tons of those. But it only has one blue-skinned, hammer-weilding, badass yordle who will fuck your shit up if you let your guard down even a tiny bit. After the rework, this needs to stay true, anything else is unacceptable.