+1 for a more generic property. Maybe sameAs or a similar name would make a difference between it and alsoKnownAs a bit more clear.
I have a use case in FEP-ef61 where a yet-to-be-decided property needs to specify identifiers that resolve to the same object. I think this is sufficiently close to the Webfinger use case, especially considering @trwnh’s idea to skip JRD.