I'd be interested in giving it a whirl, if you don't mind.<br/><br/>As far as game mechanics go, I'd personally recommend giving characters a completely new subset of abilities.  Rather than having 'sex powers/feats' as an option alongside normal ones, put them in their own category, much like 'utility' powers are separated from pure combat ones.  (Though, Feats might be able to draw from the same pool as normal Feats, since they aren't really that significant to the game.)<br/><br/>For example, a character might have an<strong>Erotic Endurance</strong>feat that gives them an 'ablative' pool of bonus Hit Points that only function against sexual attacks, or a<strong>Unusually Well-Endowed</strong>feat that makes them count as one size category larger than they are for sex attacks.  A character's kinks could also factor into this; a character with<strong>Exhibitionism</strong>might gain a small bonus for having spectators present, for example.  Powers might be things like<strong>Voracious Appetite</strong>, which allows the character to regain a healing surge once per encounter when an 'opponent' is forced to orgasm, or<strong>Deepthroat</strong>, which does extra damage and an added effect (similar to 'basic attack' at-will powers) when Receiving in the mouth.<br/><br/>The main thing is you'd want to have the 'pool' that these powers are drawn from kept separate.  Sort of like 4e's design philosophy is 'Everyone should have something to do in combat', you want yours to be, 'Everyone should have something to do in sex'.  That's my opinion, anyway.