The direction Riot's trying to push Rek'Sai will only make her overlap with Nocturne.

only somewhat. however, nocturne has a bit more ganking power than rek'sai, and he is typically built with more damage than rek'sai, who usually builds on the tankier side.

I just hope nocturne isn't touched anytime soon since I have never had a game where I went negative on him. I kinda suggest people who like old rengar pick nocturne up for the fact that hes pretty similar in terms of the ganks with old rengar.