Idea how “post migration” could work:

- New server fetches all (or limited amount) of old account’s posts and, if possible, replies
- It doesn’t post them again, but just stores and puts in new account below new posts, with mark “migrated to @user@newserver.example.com” similar to how boosts shown
- Opening that posts works like for federated posts boosted by new account

This could help avoid federation issues related to old account replies, but drawback is that because how activityPub currently works, it will not federate futher than it already did if old server gets shut down.