@potch I updated the ActivityPub ticket here:
https://github.com/w3c/activitypub/issues/422
What you're describing is a compliant AP actor, although Mastodon doesn't support it well yet. I disagree with your premise that it's hard to implement the distribution, but I'm biased, since I co-authored the AP spec and am writing a book about the protocol for O'Reilly.
I set up a static-only user at @evanp to test with. It was an interesting challenge!
Happy to keep pursuing this in the SocialCG.