Maybe the instance model isn't the right one for long term federated communities.
The primary problem here is community mobility. If any community could be, with a few key presses, decoupled from an instance and essentially plopped onto another maintaining all of the posts, comments and subscribers - it wouldn't matter as much at all. Piefed has community migration, and I assume that is ultimately the end-goal. It just needs all the major instances to read and recognise such moves.
Yeah, it's not where it should be. But I'm quite confident that such is the end-goal.
Instances will always come and go in many cases.