Bluesky enthusiasts are stating that Bluesky has ”plans” to make ATProto universal and transfer it to W3C or the like. Well, there is no evidence that Bluesky wants to give up control or the protocol is going to be widely adopted after 5 years of development so forgive me being sceptical. The story is a bit different with ActivityPub.
The whole idea of BlueSky supporting nomadic identities but the rest of the ActivityPub (plus other stuff) Fediverse being unable to do so is such an oversold idea.
A new service using ActivityPub behind the scenes (and not the AT Protocol) can absolutely support nomadic identities, even if the service doesn't treat a whole website as the actor.
It will still use did:plc, same as AT Protocol (BlueSky), but once done so, an application that understands how to work with did:plc can dereference an actor based on the DID.
That said, an existing service will simply not be compatible with this idea, without changing how it operates.
But if #BridgyFed becomes more user-friendly, that will be a big step towards interoperability. And we can finally put this silly competition between #ActivityPub and #ATProtocol to rest.