I too, am in the camp that would like to see open alternatives to the proprietary SSO function. To me this is much more than just a technology problem, however. It's a two sided market creation problem.
Email providers don't have significant incentive to become Identity Providers; Web site owners do not have significant incentive to accept persona at least until many users adopt/request it; Users are mostly unaware of Persona's existence and the argument in favor for many is rather weak as the people who seem to care about privacy seem to be in an exclusive club.
There are a few keys to success that I can think of off the top of my head:
1. Solid awareness campaign to explain benefits to non-HN type users. Would depend on solid benefits of security, convenience/simplicity, and privacy.
2. Fantastic "default" identity provider as most email providers will not, in the short term, become Identity Providers. This has to work without sacrificing UX, security, convenience/simplicity, and privacy.
3. Adoption by at least 1 major email provider (e.g. FastMail).
While I don't bring much in the way of development skills (not my strength at all), I would be very willing to help on the strategy, partnerships / business development, marketing etc. front.