I’m actually working on such a thing that will delegate OpenID to Yahoo’s BBAuth authentication allowing anyone with a Yahoo ID (and, of course, anyone with Yahoo Email) to authenticate using OpenID.
The only annoying thing is that the URL is a bit ugly. Currently, my version uses a URL structure of /firstname.lastname@example.org which is a bit annoying, but should be sufficient for now.
I’m hoping to get a release sometime next week. Stay tuned!