In my opinion the Poppy changes are completely unwarranted and should be reverted, as she is decently balanced right now. Didn't Meddler say that Poppy was in a good spot just last month? I would like to know the thought process behind these changes and if the full consequences of these changes were considered.
The ultimate change is not a "straight utility buff" as Riot Endstep has put it. The people defending the change as a pure buff to Poppy's kit have either not played her enough to be very familiar with the intricacies of her kit or playing unconventional full damage/burst builds. The decrease in the knockup duration makes the uncharged ult less effective in certain situations. For instance, an uncharged ult can be used to reposition for a stun during the 1 second knockup duration, stall for cooldowns, and delay their escape so your team can catch up during a pick, among other things. All of these use cases have been hurt by the knockup duration decrease. Furthermore, the base movespeed nerf as well as the scaling movespeed nerf on the W exacerbates the problem by making it even harder to reposition for a stun while they are knocked up. This pigeonholes the ult into just another way to deal damage during a duel, making the spell one-dimensional and discouraging creative uses for the ult beyond a way to lay down more damage onto the opponent. You might mention that knocked up enemies no longer are untargetable, but while this indeed does make the ult less prone to causing your team to miss all their skillshots during a teamfight, the knockup duration is a measly 0.75 seconds which is not impactful enough as an engage or disrupt tool (especially with the long cooldown, Note: Alistar Q has a 13 second cooldown with a 1 second knockup and Malphite R has a 80 second cooldown with a 1.5 second knockup at max ranks, while Poppy R has a 100 second cooldown with a proposed 0.75 second knockup at max rank). Albeit Poppy's R has an uncharged and charged version with different uses, the 0.75 second knockup from the uncharged version seems underwhelming. In response to Riot Endstep's comment about using the ult to guarantee both procs of Q and an auto attack, given that the recovery frames of the ult on PBE (~16 frames), the startup frames of Poppy's Q (~13 frames), and the time to proc Poppy's second Q (~31 frames), enemy recovery frames (i.e. time spent in the AIRBORNE state: ~23 frames), there is no guarantee that the enemy will be hit with both procs of the Q if they flash out (as shown in Pyrofiend's recording in this thread). Using Q before R would guarantee it, but that combo would not be optimal in most situations.
The movespeed nerf in general is something that will hurt Poppy's greatly as utility as well. Movespeed has always been a stat that Poppy has relied on heavily since the rework (moreso than most champions) due to the nature of her abilities. Even if the E range increase is considered, I feel that there is a net loss as far as the reliability of successfully landing an E due to this movespeed nerf. The change that very few people seem to be concerned with but should be is the nerf to the base movement speed. A decrease of 5 in the base movement speed of a champion might seem like a small inconvenience, but I am of the opinion that it is a huge nerf, especially in Poppy's case without a reliable dash/gapcloser (E requires a target). In isolation, analyzing the movespeed stat of a single champion is useless. The only statistic that matters in regards to how fast a champion is is the movespeed in relation to other champions. The average movespeed of all champions as of today is 337. Poppy's movespeed is being changed from 345 to 340. This movespeed delta of 5 can be seen in Janna's most recent nerf, one of the most consistent champions with one of the highest winrates in her role across multiple years. Why are we seeing a nerf of the same magnitude on a champion with abysmal pick/ban rates, both in solo queue and competitive, outside of as a Camille counterpick (because let's face it, she is only picked right now as a counterpick and because of one trick ponies like myself). Poppy's kit relies heavily on the fact that she can catch up to her targets given the lack of a reliable dash/gapcloser; increasing the range of Poppy's E while nerfing her movespeed heavily does not circumvent this problem and instead arguably lowers the overall skill ceiling and skill floor simultaneously.
I understand that statistics such as win-rate, pick-rate, and ban-rate are not good indicators of how well-balanced a champion is, but looking at the numbers, it cannot be denied that Poppy's 48.28% win rate, 2.83% pick rate, and 0.31% ban rate (lolalytics.com) points to her not exactly being a must pick/ban in the current meta of the game. In my experience, she is only used either as a counterpick or because a player mains/one tricks her. Meddler has stated that "one of our goals with champion balance is to ensure they're good choices in a wide range of contexts" (leagueoflegends.com). If Poppy is currently seen as a counterpick-only champion in both solo queue and the competitive scene, I feel that nerfing her further would only serve to lower the rate at which she is played, even though her pick/ban rate is already abysmal with the baffling amount of people I've seen say they have only seen Poppy being played once in a blue moon (does that not go against the ultimate goal of balancing a game? seeing the same 20 champions over and over again is tiring). I am of the opinion that one of the major problems of Poppy right now is that she does not excel at anything at the moment, and these changes are not sufficient to resolve this problem. She has the ability to take multiple roles and adapt to different situations, but in the end, whichever role she takes, other champions can do it better. Right now, I feel that she is in a good spot, but a weak one.
changes on the PBE? ill take anything but its just so random when shes in a good spot, albeit weak but, you gave reasons for changing 
and 
wheres 
(at least from what I've seen) has been starting
and then getting 
on the first or second back, since it helps her very mana-hungry play style, but seeing as both of these items are receiving mana sustain nerfs, I feel like she might end up being in sort of a weak state. Are there any plans to compensate 
without sacrificing anything for it, and now Mages are losing a large portion of mana and gets nothing for it?
because the amount of mana from 
isn't going to be enough for them...and this is 1 patch after you harshly nerfed Archangel Staff to be a poor item to rush and require stacking.
on every mage isn't a way to "fix" this as not every mage can really build that, and even if they do...they would be extremely useless until like 30 minutes into the game, which games don't even last that long anymore and even stalling with mages wave clear is going to be even harder because of this...which in the end makes it more snowbally.
even 
can be used to help.
Ziggs.