Yes, I agree with your opinion, it's better to add Vicky to the club in any way, whether it's being threatened or blackmailed and lan is also involved with Vicky, those two points in my opinion make the storyline even more interesting, I hope the developer can add those two pointsI mean...yeah...if the developers want to build it in, they will. If they don't they won't, that is pretty much the gist of it.
Still, I probably should have elaborated more: In my opinion the game doesn't need incest because it wouldn't add any meaningful new element to the game. We already have a motherly character with a large bust in the game that the MC can have a relationship with. What exactly would an incest relationship with Victoria add outside of that singular element that it is incest?
To me the whole "my mother did porn" angle so far seems to be more intended as an element to emotionally anchor the MC. It helps him to understand the women (especially Rose) and to remind him that they are still human beings he should respect and care for. How far the MC will actually end up doing that will - hopefully - be up to player and seems to be one of the core points of the story.
I rather expect that Vicky might be dragged into the club in some way at some point or Ian will get involved with her or something, depending on how dark and evil the story will get.