Possible rework of Crit
Hello
There are two huge problems with current crit mechanics:
- unreliability/RNG (especially when one lucky crit snowballs the lane)
- too much frontloaded damage in late-game
Reworking critical chance/damage to just damage modifier IS TOO BORING and possibly breaks certain champions. What i propose is to decrease damage provided by critical hits give champions new mechanics tied to crit OR more frequent critical hits to compensate.
Now the details:
- DECREASE of BASE CRITICAL DAMAGE from 200% to 150%
- Add SPECIAL INTERACTIONS for chosen champions (mostly ADCs)
- Champions not getting new CRIT INTERACTIONS will have +50% bonus crit chance to compensate
What are CRIT INTERACTIONS? It's basically giving unique version of Ashe's passive to every crit user, removing raw power and adding unique mechanic that rewards them for building crit in unique way, and reinforces their theme.
Champions currently using (or can use Crit to certain degree):

Champions with non-problematic crit interactions
PARTIALLY 
Crit specials for individual champions, alphabetically:
Caitlyn
Corki's critical hits always target the lower resistance. If enemy has more MR than armor they deal purely physical and vice versa
Draven
Ezreal's passive stacks now also reduce Q's cast time and cooldown based on Ezreal's Crit chance (So while his Q itself can't crit, this will allow Ezreal to turn into skill-shot machinegun if he wants to. It shouldn't be broken because there's still iCD on his TF/gauntlet)
Graves fires additional bullets proportional to his critical chance. Not chance based anymore, just tresholds where he gets more bullet - for example, additional bullet every 20% crit
Jhin can't critically hit unless its his fourth shot. His fourth shot has +50% critical damge ** So he can't crit except for his last auto, which deals same damage as it does on live. Tweak his passive if he ends up weak.
Distance covered by Kalista's jumps inceases based on critical chance OR Rend deals more damage based on critical chance. both are pretty boring tho. Increasing Sentinel's damage by crit would be very interesting option, but unfortunately it would lock her to "PREMADE ONLY" mentality even more.
Lucian's Lightslinger will always crit if triggering attack crits, and its damage is increased by his Critical chance** (So if his AA crits, his lightslinger will do MORE damage than actual AA if is his crit chance high enough)
MF's attacks bounce and hit target behind enemy as well (basically her Q mechanics) up to 2 times, based on her Crit chance. Might be too strong but she's AOE-ish ADC and her R damage suffers alot by building crit. Could provide interesting synergy with her current passive.
Increase stack amount on Tristana's Explosive Shot, and her critical strikes now count as 2 attacks when calculating damage from Explosive Shot.
** Tryndamere can no longer crit, however rage gained from basic attacks is increased by his Crit Chance. When Tryndamere uses his Q, his next AA will deal up to 400% increased damage proportionally to rage spent. Rage now depletes much faster and at all times.** Rage gained should have very high Crit scaling, he should be getting full rage with 1 AA at 100% crit chance
Twitch can't critically hit and his passive now deals physical damage, but its damage is drastically increased by crit chance. His poison ticks can crit, dealing slightly more TRUE DAMAGE instead. Basically much less up-front damage and much, much more over-time damage. Might be fun, he could turn to "poison sprayer" instead of "the only use of my passive is to trigger E"
**Vayne's attacks can't be critical hits, but her Silver bolts damage is increased by crit chance. **This means Vayne will deal monstrous damage to CHAMPIONS with full AS+Crit build, however she will struggle against turrets/minions/mosnters if she doesn't build AD. Also guts her ability to lifesteal
As you can see, i don't have idea for some champions, but im sure you will be capable of contributing with ideas.