The idea of not telling your biological daughter that you're her father and then proceeding to pursue a romantic relationship with her sounds pretty rapey to me. So I think the number of taboo elements will increase instead of decreasing since instead of only incest, it will be rape+incest.
Seeing as how there are games with 'sleep sex' tags, but not rape, I don't think there's any chance that's going to count as rape genre. I'm not even sure I'd consider that rape in real life, I mean, if a woman is looking for marriage and you convince her you are too only to have sex and ditch, is that rape? I wouldn't count it as rape, although obviously it's extremely fucked up... and deceptive incest is even more fucked up; not sure what I'd call it... sexual deception? I wish we had more words for different tiers of sexual crime.
EDIT: Oh, btw, just to stay on topic with this thread, I tried this game out dev, and it's absolutely amazing.... these are some of the best renders I've ever seen in a game. The 'stalking' sequence was really awkward and didn't make much sense to me at all and there were a few cases of weird dialogue, but overall was really great! I guess also two of the women in the game are hardcore coomers, which might bother someone if they were looking for more believable setups for sex scenes, but I don't mind that. Great job!