i think it's really cool that ADCs are going to have lane and item diversity

item changes would be a good start, tanks need to exist late game instead of being awful early, mid-game gods (if they're ahead) and then most of them dropping off in being little more than CC bots outside of Malphite and Rammus against AD comps

giving them new items or changing existing ones to encourage stacking for tanks rather than being easily abusable by bruisers as has been the case in the past (Warmog's for example requires that you have a health threshold, this could be done with other defensive purchases), as well as creating situational damage items to give them power spikes for brief periods of time (like an active, or something that has to be activated in combat similar to Sterak's). items that boost their defensive stats, the tank version of IE or deathcap.

some tanks probably deserve a small rework like we've seen in the juggernauts and marksmen, possibly to differentiate their roles and emphasize what makes them unique

i don't think Darius is too awful for some tanks, though they aren't ever the best pick against him as they can't bully him out of lane

it's mostly how poor a lot of them tend to be at clearing waves that they just get pushed in, or they're extremely vulnerable to ganks and often get punished with poor base stats, too