I hope that the possible Kha'Zix changes for the assassin update
are aimed at actually making him adapt to the situations instead of having set on stone evolutions.
This is because right now, Q and E are mandatory evolutions, with W and R being mediocre options that you only evolve late game because there is nothing else to evolve that could be better. And people almost always evolve W because evolving R is so situtional (ever since they removed the damage reduction) and W at least has general uses.
To be honest, I don't even remember a time where there wasn't an evolution that would be the strongest, allowing players to choose the evolution that they wanted, depending from the situation. There is always the strongest evolution. Back then his W was the strongest, when it applied Kha's passive. Then, Q was the strongest because it did extra damage based on missing health and it was really easy to get isolated targets. Then R was the strongest due to the damage reduction. Then W was the strongest because of the utility, lower cooldown and higher damage when compared to nowadays. And now, Q is the strongest due to the majority of his damage being focused on the evolved and isolated Q. And between all those times, E was always the strongest option to evolve second, because the extra range and resets are simply too good to pass up.
A good way to solve the problem of his Q being mandatory would be to split his damage between his passive, Q, and W (nerf Q, buff passive and W), while making all them do bonus damage to isolated targets, instead of only his Q. Then, they could give different benefits to each. For example, his Q having a way lower cooldown with his W having the range advantage.
His E is mandatory because you get resets and extra range with the evolution. There is simply no reason not to evolve this second. There are even some situations where you could evolve this first, the only reason why most people don't do that is because Kha really needs the damage from Q. That said, I don't really think of many ways to solve this problem, other than making the unevolved skill itself have the resets (and possibly the extra range) while giving a more situtional bonus to his evolved E. This could have the side effect of overbuffing Kha'Zix's early game, however, in addition to making his possible E evolution undesirable, depending from what they put. There may be better solutions to this problem.
All that said, I just want Riot to actually make Kha'Zix fit with his lore, where he adapts to every situation that he finds, instead of having the set in stone evolutions.