In the absence of a singularity, I would not expect this to become widely accepted within my lifetime. I'd say polyamory is the next type of relation likely to become tolerated and that is still at least ten years off. Incest is probably only slightly less despised than pedophilia, but I've seen pedophilia frequently equated with murder, so that's not saying much. Bestiality is probably the least likely thing I'd expect to become accepted. None of these three are going to happen within a timeframe I'd feel comfortable making predictions about, but never is a really long time so who knows.