It's open source, if you care that much, swap it out yourself.

I have the opposite reaction: I only want to use my Google account to sign in. If a site doesn't have that, I'm less likely to use it.

Would you be more likely to use Persona if it acted as proxy to your gmail account, as it does on http://beta.123done.org?

I have no idea what persona is or what it's for. I'll look into it at some point and see if it can be integrated.