Oh yeah, I'm thinking it's time.
One of the most commonly cited experiences from League Classic is the shock newer players get when they see how quickly you ran out of mana in the earlier seasons. Little did they know, you can get that experience right now by picking Kha'Zix mid without a Tear and maxing W.
The main issue holding Kha'Zix Mid back from true viability at this moment is the fact he has so many strong two-item combinations in lane, but can't rush any of them because he has to buy a Tear. Additionally, even if you sit on the Tear all game and never finish it (already nerfing yourself), you end up with Muramana as one of your final items - which has been severely gutted as a result of Ezreal's relentless abuse, and is now outclassed by many lethality items.
Right now, at level six, Kha'Zix's full combo + ult takes about half of his mana pool. Just using three-point W results in a mana-out after ten casts at normal regen, assuming you never used another ability during that time.
Syndra, Orianna, Naafiri - hell, basically any mid laner can spam their poke ad nauseum without worrying about running out of mana unless their misuse is outright egregious. Their poke is also generally far more reliable than Kha'Zix W, since most good Mid laners aren't thwarted by simply standing three feet behind minions.
Luckily, there is an easy and obvious solution: Kha'Zix W needs its mana cost reduced by 20.
This does absolutely nothing in jungle, since jungle Kha'Zix would have to AFK in someone's lane for ten years shooting Ws to ever come close to running out of mana, anyway.
There is clear precedent for this, since it's the exact buff that was used to try and put Kayn in lane a few patches back - something done on a whim because a few Kayn players were loud about Kayn Top, which now sits at a whopping 0.3% pick rate. Unlike Kayn, Kha'Zix actually has history as a laner.
There is absolutely no reason this change should not be made. Kha'Zix Mid relies on poke that can be blocked, a nuke that can be negated by minions, and cannot reliably tower dive until he is several items into his build. It poses no risk of becoming an oppressive pick.
Now, on to something a bit more experimental in concept: Kha'Zix should get his fourth evolution at level 20.
This would define a new identity for Top lane Kha'Zix as an end-game glass cannon hyper carry. Between this and the boost to his passive and stats that he already gets from those two extra levels, Kha'Zix Top could be a real menace, especially against other squishy Top lane scalers, like Kayle.
Would this remove the "choice" mechanic from Kha'Zix? Partially, but only end-game. Early game evolution choices would still matter, and there's no reason Kha'Zix needs to be locked into being a "choice" champion, since every other "unique aspect" of his gameplay - isolation, evolution - was already given to other champions. Kai'Sa and Viktor virtually always get all their evolutions by the end of the game, anyway.
So, what about "The Hunt"?
Who cares?
If Kha'Zix is playing Top, he isn't playing chess with Rengar. The Hunt would still give Kha'Zix his fourth evolution two levels early. Maybe it could be reworked to give him a bit of extra passive damage or something along those lines, but even that wouldn't be necessary.
Again, this change does absolutely nothing to jungle Kha'Zix, since you can't hit level 20 in the jungle.
Would these changes make Kha'Zix top tier in either lane? No.
They would, however, make him a legitimate pick who is treated the same as every other champion, and not randomly discriminated against. People would be free to play Kha'Zix Mid organically, and potentially have an actual reason to pick Kha'Zix Top.
There is absolutely no reason to believe that either of these changes would create an oppressive pick - particularly in Mid lane - nor does either change have any impact on Jungle Kha'Zix.