I like it, definitely would be an interesting direction to go, though I wonder if the current game engine would be equipped to handle it. It might be something to keep in mind for "Sex Sim 2: The Adventure!" or something like that, otherwise.
I am reminded of the open world aspect Bonetown had, that was a fun example. It had minigames and challenges you could do in addition to the story missions, using various characters randomly generated within the assigned area. Sometimes you had to bring a specific partner to orgasm as many times as you could within the allotted time, or you had to nail as many different ones of a certain type as you could (one funny one went by weight level, kept track of how many pounds' worth of partners you went through, so the fatter the better).
It also had a "fantasy room" bonus area, separate from the main game, where you could go and revisit all of the special sex encounters you'd unlocked via the main story missions, and also had a good amount of random hotties lounging about for you to have fun with. Something like that seems like it could be doable, would be a fun option.