They should be interoperable... I should be able to take my account from bluesky and host it on any other pub server

The server shouldn't need to be specific to mastodon/bluesky networks either

Ghost (the blogging platform) is kind of a peek into this — you can host your microblogging account there and interact with other activity pub networks like mastodon

this is the promise of the activitypub standard, anyone that uses the standard can interact with anyone else using the standard...