A UI designer’s dream is a backend engineer’s nightmare
Without knowing much about Lemmy I would guess that a bit more info is needed, along with some human interaction on both servers to validate the move.
When I signed up i wrote a bit about why I chose that server, I think that as a minimum would also be required.
Edit: I would also only allow moving between servers at the 1st of each month, just to cut down on work for the admins.