Do you have examples of sites that don't use Persona as the BrowserID implementation? I'd like to see how sites are handling the user prompt when there are going to be alternative providers to Mozilla's Persona service.
Doesn't work that way; Mozilla's Persona service just serves as a shim for browsers without native support for BrowserID. On browsers with native support, Mozilla's server won't get involved at all.
No since what I do is pretty experimental side projects and fine to just use the persona end of things. Also I don't currently have anything public running right now myself (as it just entered beta so I won't release until v1.0).
If you haven't tried it out yet I encourage you to do so...it only took me 30 minutes to get up and running the first time around.
