What I would like for Kha'Zix
Simply speaking, it would be a buff to his ult along the lines of
IF khazix evolves his ultimate, and if his q is evolved, then the following change would happen. If the previous conditions are fufilled and if khazix, attacks in stealth (not after is ends), then the attack is treated as if the target is isolated.
For an assassin, his ultimate is quite lackluster, and his main source of damage relies on his opponents misplaying, not any real skill on the players part is get them out of position. I feel that this would give khazix a bit of reliability in the late game, as his ult is not evolved till last, if ever, due to q and e being much more important.
This means said buff would only really affect his late game as he would finally be able to do something during a team fight instead of just cleaning up after a massacre.