If you don’t own your historical data, and don’t own your identifier, which is exactly the case right now, fediverse becomes just a standard for smaller walled gardens to talk to each other to expand their content base. I think this migration problem can be solved by identify proof (fep-c390) and object integrity proof fep-8b32? After that it’s just exporting and importing to a new server/service and let your followers know that you moved.