Why limit your list to just U.S. cities?
I have made jokes in the recent past about franchises rotating around to various cities in the United States (future ideas for new teams: Las Vegas A's, Oakland Devil Rays, Tampa Bay Twins, Minnesota A's, etc.) and how that just would not make sense, big picture.
But lately I am keeping a more open mind about things.
I think we have to recognize that there are essentially no ironclad rules anymore, no binding leases, no normal ways of doing things, and anything is wide open to possibility. Particularly think about how MLB seems to want to emulate the NFL; and that league will move a franchise in a heartbeat. I agree with you it is unlikely, and also I commend you for leaving the open possibility that we might turn out to be wrong about this.