Kha'Zix is just not in the Meta. He can't fit the jungle, he can't fit anywhere.
Kha'zix currently stands in the top 5 lowest win-rate champions. The jungle doesn't help him at all because of him being super squishy. Trying to isolate a camp to do the clear faster only makes it harder to kill the camp and you lose a lot of HP making his early game horrendously weak. Kha'zix is way too reliant on isolation to even do damage, so he can be outpicked easily by other junglers. Also the rise of tank junglers makes Kha'zix too easy to counter and only just makes it more difficult for him to keep up. He as a overall champion can't do much in helping the team except picking off kills himself when someone is roaming (Which he is supposed to do), but if you compare him to other jungler assassins, I.E. Rengar, he is much stronger in the jungler has LOTS of options in his kit than Kha'Zix. If you Kha'zix top lane, he is already out classed by majority of the top laners because of his weak dueling power. I think Kha'zix has a strong kit in terms of damage and mid-game power, but he doesn't have enough to fit the meta :(.
Possibly a Kha'zix buff next patch?

after my 3rd game. (And to add more insult on his part, I went 16/3 with him and have yet to remove him from my roster of champs I play)