It's not an option, but there *is* already a full incest relationship going on in the game (and it has been going on for a long time). Frank just hasn't realized it yet.It's a shame it's not an option, I against the idea of taboo IRL but in these games it's a nice brake from reality, the huge buildup with Abby would make the taboo possibility nuclear when/if 'it' happened.
And Abby's time is coming soon anyway, that's for sure--the only question being, of course, how far-off "soon" is, lol (full-on sex will probably be a few updates yet, but things should start heating up quite a bit between them, well, "soon", the way things have been progressing).