Good approach, I approve. Constant feedback loop with a consumers is the best. I wish I had one (developing non-games non-adult software as of now).
Some more feedback below. Can't be sure if it's totally game-related or OS-related though, since I run it on Linux

Maybe game-related if it's reproducible on other people PC's with a Windows, if they'll quote what I wrote.
The bug is reproducible on my side.
Also, I encountered a bug with the MC model dropping the walking surface somewhat, with the viewpoint when walking becoming on the level of other character's legs. I don't remember the exact conditions, bcuz I clicked something very fast out of the dialogue (or maybe out of a sex scene) with a character.
And I believe the "entry point" (or entry area, I dunno how it's implemented in a Unity\C#) of a dick for anal penetration in the MC's bedroom should be somewhat lower. For some other scenes where the female is on her back - it's the reverse often, should be higher. Again, I strongly recommend to take a look at TValle's work (Some Modelling Agency), the guy must've worked at some physics degree for a PhD or seriously researched these things - his implementation of penetration is VERY immersive, feels way more natural. Your current "entry point" makes the dick and characters bodies textures clip into the each other where they shouldn't have been seen and thus it ruins immersion - the most important feeling you're trying to create when you're trying to make something people like. And the area they cover is too large I think.
Moreover, the penetration itself is somewhat weird - I see that dick gets "stretched" and "thinned" visually during an insertion inside, it is especially noticeable on the "auto-mod", when you increase the speed.
Maybe these things aren't included in what you mean by a "core mechanics" and can be improved much later, but here's what bothered me personally so far in a demo.