This stands a very big risk of creating consistency collisions and other immersion breaks when they continue acting along their pre-set ways when not under our control, but can suddenly decide to do something complete opposite of that because we took brain control of them for a conversation... On the whole I think controlling anyone but your main character in conversations is a flawed move, which stands to create more problems than it offers opportunities.
++ your entire comment, but double ++ to this part in particular. Writing this stuff is hard enough, and creating mechanics that add this kind of complexity is - at a minimum - fraught with pitfalls
This next bit might be a little stream-of-consciousness, but I think it's got a good shot of speaking to the topic ...
What I like about crpgs is that they create a defined world with defined rules. Full love and respect to people that hate metagaming, but I'm not like that. I love metagaming. I love using a clear, defined, and established ruleset to optimize for the world I want to participate in (and to try variations). Real life is sufficiently a motherfucker as it is; I want my recreation to feel like I'm accomplishing something, and if that means groking the rules and how to exploit them without fucking up the story, all the better.
For companion romance, playersexual npcs are ideal in that regard - you can build the world you want and incorporate them or not as you choose. Maybe a minority of available companions have anatomic or chrotosomic preferences, but that's just for texture.
I liked the way PoE2 handled this, where there were I think 6 available companions, two aren't interested, and I think only 1 or 2 cared about the contents of your drawers. The mechanic was a combination of sharing similar values (in a much clearer way than "approval" here) plus as someone else mentioned above, relevant dialog options to clarify intent.
