Crazy Idea - Replace Crit with Energized
Hear me out here.
Critical Strikes have a strange buildpath at the moment. You can never get 100% crit rate - you have to settle for an ignoble 90% (by building 3 zeal items), or 120% (by building 2 zeal items and Infinity Edge). Most people just stay at 60%, and don't bother going up any further. The only way to enhance the potency of your critical hits in any way is to buy the afore-mentioned Infinite Edge, which converts some of their damage to True Damage.
Additionally, what's even stranger is the Energized mechanic. The only way you can get Energized attacks is by taking a specific keystone (Fleet Footwork) or by building 
. What's interesting is that every fully completed item for Energized also gives Crit. As for how the mechanic works, you build up Energized stacks by moving or attacking, and when you have enough, you discharge them for extra damage/healing.
What's also funny to look at is 
. Stormrazor builds up charge by not attacking, and gives you a mini-crit when it's at full charge; as you can see, this is remarkably similar to Energized attacks. It's almost like someone at Riot decided that Critical Hits were either too consistent or too inconsistent, and decided to try out a new way to handle them - like Energized attacks.
In my opinion, we should phase out the chance-based Critical Strikes entirely. Instead, we should enhance the depth and variety of Energized Items. So, what does this look like in practice?
Items: Well, the point of this is to provide more complete and interesting build paths, and remove randomness from the equation. My first suggestion would be to change how Rapidfire increases the speed at which you charge Energized - instead, make it so that each item that makes your attacks Energized also makes Energized charge faster by 10% or so - then, by stacking a few of these items, your Energized attacks will come up more and more often.
As for other items you can make, there are tons of options! The entire point of Energized attacks is that they give you more utility than just damage; Rapidfire increases your range and lets you hit Energized attacks on structures, and Shiv gives you waveclear. You could have a new one that gives the energized hit a slowing effect, and change 
so that it makes your energized attacks deal some percent true damage.
You'd obviously need to change 
and 
(because crit no longer exists). Instead, you could have them build out of 
or 
for the AS, and possibly even use 
or 
as components. This way you can add more CDR into the ADC build path, while also providing different options to get AS for ADCs with various playstyles. You'd also want to change 
, but that could probably be solved by changing it to a larger damage reduction on exclusively Energized attacks.
Champions:
If you remove crit, you'd also have to change how some Champions work - notably 
, 
, 
, and 
(off the top of my head). To be honest, I think that Caitlyn and Tryndamere could be adapted to fit Energized attacks fairly easily. Ashe could probably just have the entire Crit aspect of her passive removed, and edit it to enhance the playstyle of "Hit enemies to slow them, then hit slowed enemies for further slows and extra damage".
Yasuo would probably need some major edits for his passive. In the game, his passive effectively boils down to "You get large amounts of consistent damage in return for building an AS item with no AD." Because of his passive, Yasuo doesn't have to worry about rushing something like Phantom Dancer that gives no AD, because he gets a massive spike of power just by getting lots of free crits that are slightly less effective. To compensate for the removal of crits, he could probably just get something like Jhin's passive - except scaling harder, and only off of AS. Not a Yasuo main, this is all conjecture.