The only ones that would sell would probably be the men changed into women. The women being men would just be utterly disgusting and probably wouldn't profit.
Female Braum? Hell yes. Male Nami? I'd want to punch the creator..
Male
might go over well?
Never, reason why this idea would never work for skins, is because Riot would have to redo EVERYTHING. Voice and animation, and that takes too much time just to gender bend champions.
I really just want Princess Ezreal, gotta keep the Haruhi dance though.
Though to be fair we already have Debonair Vi, that's practically a gender swap skin, I don't know how much manlier the champ can get.