Just played the demo, and it looks like the beginnings of a potentially very interesting game. Your comment about planning to implement route choices via gameplay instead of dialogue options appeals to me in particular. Reminds me of when my mind was blown upon first finding out how Dishonored subtly shifted the game world (and later unsubtly shifted the whole story) depending on how you played.
However, if I might make a recommendation, giving little "hints" to Aster's activities in the dark after leaving the dungeon (like the dialogue, small changes to her model like semen stains, pubic hairs and whatnot) would add a little bit to the mystery NTR aspect as the MC starts catching wind of what we, the players, are already seeing in the dark.
I also do like the possibility of adding a NTR->NTS route separate from an oblivious-NTR route, but I'm not sure how you'd implement the choice via gameplay instead of dialogue choices. Would we have to catch Aster and Mentor in the act X number of times with a new mechanic or something?