gender swaps (although, actually, no fandom I can think of has canonically done this)

Are you considering genderswap to be "mind in the same body but the body's now the opposite gender" or "mind now in someone else's body, and that person is of the opposite gender"? Because if it's the latter, I present to you: FARSCAPE.

(Pretty much if you ever think something wild and crazy hasn't been canonically done, Farscape probably did it. :D)