Yes, I've thought of yet another novel idea that I may or may not ever write. Like The Third Face and its coming sequel, it's a story that features multiple personalities.
1000 years in the future, people are packed into bodies, not homes. Childbirth is restricted, and most population increase is done by artificially creating new personalities within existing brains. The rich get their minds transplanted into good-looking or athletic people, while the poor are relegated to crippled or diseased bodies.
This setting is all I have for the story so far, but I think it's an interesting enough approach. It's definitely not a thing like The Third Face, that's for sure. It'll take some extensive character designing in order to actually work. I hope I get the chance to write it, because it seems exciting to work all that out.
I don't know why I keep having these ideas, because I've never met anyone who actually has multiple personalities. The most exposure I've ever gotten to it was in a high school psychology class. There has been no movie or book I've ever looked at that covered this at all. It's actually a complete mystery.