Interestingly, if you buy if from Itch, you get the Humble Store downloadable package (no Steam key), but if you buy it from the Humble Store, it looks like they offer a Steam option there.
Momoroda III gave out Steam keys to Itch purchases, if I recall correctly, but that doesn't guarentee they will again.
I just went ahead and picked it up on Itch; if I get a key to add it to my Steam library, even better, but not the end of the world for me.