@grishka The problem (?) is that I could configure my WebFinger server to point to someone else's actor endpoint, which would be misleading. So if evan@domain.example points to https://whitehouse.example/users/potus, it would make it seem like evan@domain.example is the right shortcut for getting to the President of the United States's ActivityPub endpoint. (It will happen.) It's not *that* big a deal, but it's a little bit of a problem.
@grishka What we need is a way for the AP descriptor to say, "these are valid Webfinger strings to use for this account." There's not a way to do that in the AP standard (yet; I'm going to start working on a FEP for it).