A Way to Open Up Bottom Lane: Add More Push Mages
I think adding more Push Mages to Bottom Lane could actually add more diversity to Bottom Lane other than just adding more Mages to Bottom Lane. Why? Because certain Melee Champions ACTUALLY counter Push Mages, such as Super Sustain Melees and Assassins. Aatrox could find a spot in League by countering Push Mages that will waste away their mana trying to poke him down while not having the same issues that he has in Top Lane. So how can we add more Push Mages? Well...
Azir
Prime example of a potential Push Mage. By adding back his power to "Burst Shot" towers with his W (or some other way), we could move him to Bottom Lane so that he could have a healthy lane. How is it healthy? Well, Bottom Lane actually has a LOT more sustain than Middle Lane meaning his Zone Poke can be undone through Life Steal and Heal Supports (who currently aren't that big right now as well). This isn't to mention his Passive synergizes perfectly with this kind of role.
Karthus
Perfect example of another potential Mage that could be added to Bottom Lane. Maybe his Q now deals 15% damage to towers if he is within tower range, increased to 30% if there isn't an enemy unit within the tower's range. Karthus could easily also buy a Lich Bane for CONSTANT procs to kill towers if he was better secured into this role.
Malzahar
Plain and simple, make Voidlings NOT prioritized like towers unless they have damaged an enemy champion in the last few seconds (although under normal circumstances Malzahar would be targeted anyways). This way Malzahar offers a more unique Push Mage feel in that he uses his E to shove the wave and then kill their tower with his W. This could redeem Malzahar and push him somewhere that would make him have a better performance overall. Something could would be if Malzahar's E could spread to towers or be cast on them, but not deal damage to it. This would make Voidlings prioritize the tower without adding significant damage potential his tower pushing.
Taliyah
I think with some changes, Taliyah could be put into this role. Since she has some decent sustained damage, I think with an extra push to increase her damage to towers, she can be made into a potential Push Mage. Perhaps making her Q be able to deal modified damage to a tower once per Q cast (not bursting a tower with a full Q).
Heimerdinger
Similar to Malzahar, but with stationary minions to make it a lot different in how he interacts with the lane. With a complete rework to his turrets while still making them stationary (at least mostly), I think he could easily become a Push Mage due to his sustained damage nature and potential for his turrets to be able to shoot towers. Perhaps a direct hit with his E could make the enemy tower have reduced attack speed, although that might be too much.
Aurelion Sol
Plain and simple. Aurelion Sol would be cool if he could potentially push towers with a moderately modified kit (which they plan to give him, similar to Shyvana). Aurelion Sol would be nice to bring Bottom Lane since he has nice sustained damage. Maybe if his stars dealt modified (25-40% based on level maybe) damage to towers while he is within the tower's range.
The best part is Ziggs would still maintain his niche since his ability to W towers would still make him the best for specifically killing towers as QUICKLY as possible. Plus his long range would make him safe even if others get near his push potential, meaning even if other Mages were tried out in Bottom Lane, Ziggs would still have purpose to be there over the others due to his long range and heavy AoE nature.
With this meta shift, some ultra sustain, sustained damage Melees would even get a chance to be seen in roles other than Top Lane, which usually makes them a pain to play against. The problem with these kinds of guys against ADCs is that an ADCs poke is limitless so they basically have to infinitely sustain to be able to be good, which makes them unhealthy in Top Lane against other Melee champions. However, if they get moved to Bottom Lane, they would still have the Melee v Ranged disadvantage, but Push Mages would have a limited supply of poke due to mana that would make these ultra sustain Melee champions have purpose outside of annoying endless sustain. This includes the likes of:
That's right, the some of the usual farm fest, uncontested, hard to balance Melee Carries of the Jungle might want to go Bottom Lane with the right meta shift due to the OVERALL increase in potential gold from minions instead of monsters. You could get the human chainsaw of Master Yi on your team without having to give up that position for a Tank, Gank Heavy Champion, or someone else.
"But this has all popped up because of how WEAK towers are! This shouldn't even BE!" A good insight, but I do not find this opinion to be because of how easy towers are to kill (although I have never found a MOBA where towers are very hard to kill due to strategies naturally popping up for killing them). I think it has popped up actually due to how low protection the towers provide against a dive. I think the best solution to this would be to make towers deal % Health PHYSICAL damage to champions. This way Divers, Bruisers, and the like that don't invest into Armor and just get a bunch of health will be punished more for recklessly tower diving. Plus, I think towers could have their AI modified to be less "abusable" so to speak.
"But this will just center the game more around Bottom Lane in general!" This is less of an issue in Bottom Lane itself, but more in how useless the Top Lane is as far as objectives go. It's much less "OH NO" when the enemy team gets Rift Herald than Dragon because you know once teams begin to group that the buff is just a 5% reduced damage against champions buff. If Top Lane was made more important Early Game, then this whole "Bottom Lane 5v2 Early Game" issue would be solved. Not necessarily by removing value from the bottom side of the map (although I DO think Elder Dragon should be harder to kill and be similar to Baron where it demands commitment to kill).
TL;DR I see a lot of potential in Bottom Lane if Riot pushed more Mages to try and lane in Bottom Lane through changes in their kit. A lot of Mages currently aren't played and most of them could see play if they were modified slightly to have their kit fit into the Bottom Lane scenario currently.
might also be an interesting proposal since her E effectively acts as ranged DPS similar to a Marksman.
Maybe similar to Malzahar, have it to where her E can be used on towers, perhaps at a reduced damage rate.