Yes, though doesn’t it seem crazy that we’ve had to wait for same-sex pairings to mix up the lead/follow. Is there any reason a mixed sex pair couldn’t play about with those roles too?
It's because the steps are codified. I'm not sure there's actually a specific rule against it, but because when you go onto the floor you present yourself as a lead and a follow, then you do the steps the way they're described for a lead and follow.
I think it would definitely hold true for restricted step competitions (by switching you're doing something that isn't defined in the steps you're allowed to do), in open choreography it might be ok? The big issue I can see in ballroom though is that you're not allowed to break hold, so you'd have to find clever ways of switching.