Give turrets a MINIMUM damage of 10% of target's max HP as true dmg. This means no more tanks tanking 30 turret shots. They can tank 10 shots, maybe few more with shields
This also prevents squishies from free tanking turrets since the 10% damage is the MINIMUM damage.
Thoughts?
so your plan is to give the middle finger to everyone who isnt mobile and bursty enough to only take 2 turret shots on a dive before he flashs/dashes back out of range?
op is 
main it seems.
if you really want to buff turrets, just get rid of the ramping up damage bullshit and have them deal full damage from the first shot, so you actually NEED a tank or fighter to tank a turret for you and not every squishy adc and assassin can dive your ass at lvl 2 as long as theyre mobile enough to only take 1 or 2 shots.
Nobody wants to see first turrets staying up until 30 minutes in just because a Sivir is clearing all the wave.
This would make a few champions, notably Maokai right off my head, quite less significant than what he is right now. Not all fights are done in turret-less grounds. Teams need to seize the opportunity and have a tower dive fights here and there, and this is what certain champions excel the most at.
If you think you're gonna get tower dived and beaten badly, LEAVE the tower.
edit: if your entire team is at the point where "we lose fights even if we fight under tower full 5v5", then you probably screwed up your early game, or your team composition is horrid and the win was well deserved for the enemy team.
Towers definitely need at least unlimited scaling. Each shot after the first should do like 25% more damage than the previous one. No champ should be able to tank more than 5 shots without being full tank build.
There needs to be real risk diving a tower, at the very least until late game.
5% on outers, 10% on inners, waves of 10% MHP true damage once every second on nexus?
Works on super minions
I'd like if at least the third tier turrets had this effect. That's where getting dived is the most terrifying.
I don't think towers as a whole are supposed to be equally impactful from early to late game
