The problem with these types of redundancy schemes is that it simply takes a Internet backbone hiccough (or AWS fuck up) to cause there to be multiple primaries (i.e. lemmy.world is online still, but some portion of the internet can’t see it, so a replica promotes itself to primary, people use both, how do you reconcile it).

This is not even beginning to talk about the nightmare scenarios possible if someone hacks a replica.

Edit: Still, this is a good thought and similar to how some actual software packages do things.