This would be cool regarding the current scaling problems with too many users choosing the same instance (it would make “distributing” the load easier my making it possible to move already created, existing accounts, if the user wishes to), and also would it solve the problem if an instance is to be shut down for whatever reason, people also could “take their stuff” and go “somewhere else”. Let’s see, maybe it’ll be possible in the future.
Yes, it does offer importing from Trello: In a “project” (i.e. a collection of boards), after clicking the plus-button to add a new board, you can either just give it a name and create an empty board, or your can click “import from Trello”. I haven’t tried it, though, I’m not a Trello user (because why should I; I have Planka, haha). You can probably try out the import capability with their demo instance.
Have fun with your self-hosting adventures!