Thank you all for your input! You're giving me a lot to think on.
I feel like flipping them back and forth between bodies/pcs as I feel like playing two completely different characters and campaigns would get really confusing for my players really quickly. I suppose the thing I'm most...
I absolutely want them to create the characters they'll be and I'd never put them in the bodies of characters that I thought would be overly distressing for them. I just don't know how to exactly present that without spoiling the swap. Like, maybe have them come up with one complete character...
So, I'm gonna say up front that I've never been a DM/GM in my life. I'm looking for some guidance, maybe somebody to flat out tell me this idea is bad if it is. But I thought it was cool and want to develop it to the point where I could comfortably present it to my group as a possible campaign...