Actually, it won't. You'll OpenID auth into google.login.persona.org, and then get a straight up Persona certificate signed by that fallback, along with all of the privacy safeguards that has.
Honestly, we haven't quite figured out a good way to do a "beta" or partial roll-out for this without breaking other users. Yaaaay decentralization! Instead, we'll be extensively QA'ing it in testing environments, and then we'll flip a big switch to enable it for everyone.
We wouldn't even have to turn it off -- as soon as gmail.com can vouch for its own users, the protocol automatically and preferentially switches over to that. The centralized parts fall away on their own whenever they can. :)
