I think it's possible to do good sex scenes in FPP. Probably more difficult, sure, but possible.Also lets not forget, sex scenes are FPP... so its really just gonna be an awkward closeup of some strangers face convulsing and grunting.
Did you ever play/see the sex scene from Far Cry 3? If so, I'm curious if you thought they worked. I'd post a youtube link but not sure if that'd be allowed because...bewbs.