Riot Games are adding some sweeping changes with the new item overhaul and one of them is a blanket nerf to critical damage that may or may not be made up for by mythics and changes to old purchases.
Mark "Riot Scruffy" Yetter posted another preview of the changes that are coming soon to PBE, prompted by the item overhaul. One of the most important changes is the reduction of critical damage which will now have 175 per cent multiplier instead of 200 per cent.
Currently, there seems to be a light at the end of the tunnel for AD carries that want the same crit multiplier as before and it's called Behemoth Slayer . This mythic will increase crit damage by five per cent for each legendary item in a character's inventory. Since boots and Behemoth Slayer itself will take up two slots, the crit damage can be grown back to 195 per cent which is still lower than before but at least it's not that bad.
On top of that, the critical chance itself will be harder to come by since individual items will grant 20 instead of 25 per cent. In other words - if you want 100 per cent crit chance, you will need to build five crit items besides the boots.
The bright side is that some items that didn't have crit chance stat will get it when these changes come along. Mercurial Scimitar, Bloodthirster and Mortal Reminder have been mentioned thus far which means ADCs will still have some room for build diversity.
As far as champions like Tryndamere, Yasuo and Yone go, there will be additional changes to their kits that will aim to compensate for crit itemisation overhaul.
When it comes to bottom line, it appears that Vayne and tanks will be on the receiving end of these updates. Everyone will have access to a passive similar to Vayne's, thanks to Behemoth Slayer, and she will either have to build it as well or just opt for dealing less damage than carries with that particular mythic item.
As for the tanks' issues - well, what could be worse than Vayne for them? Every ADC becoming Vayne.