One thing I repeatedly ponder, in the ActivityPub based Fediverse: How do you meaningfully handle fallback accounts? Not that it really is needed most of the time, but: Posting a reference to a "backup account" to your profile doesn't seem of much help in case your instance is really down and offline for an extended period of time so how should someone figure out? And, adding to that, federated platforms differ very much in the information they choose to (not) fetch and display from remote instances, so chances are that additional / custom metadata fields that, in example, Friendica people merrily rely upon don't even show up for other users...