It's a possibility, but it's also a risk to actually make the game quite a bit worse for new players. If a player messes up the correct incest relationships, because he doesn't know or care about the incest, the exprience may potentially be bad and the story will make less sense than it should. Sure, there are some games which have some kind of background code for this case, but that wouldn't be possible here, so it would be 100% up to the player to get it right. Imagine someone typing in "girlfriend" instead of "sister" in Jenny's case...
That's why I usually prefer the patch solution, simply because it doesn't compromise as much. You have a pretty clean and playable non-incest version and it's possible to install the incest without having to worry about the context.