Disclaimer: I work for Mozilla, I maintain django-browserid (and StravosK is a valued contributor many sites. This is all just my own personal opinion.
I was very bullish on Persona early on, but the fact of the matter is, we failed. And not just because (as I feel is being implied) some higher up suddenly came over and asked for an unreasonable amount of adoption for a revolutionary product.
We failed for a thousand reasons. It should've been supported directly within the Firefox chrome ASAP. It had branding different than the site you logged in to and was in a popup[1]. It took the name of another Firefox feature that users already knew about. Because the team was experimenting fast, the code quality of the service was such that outside contribution to it (or even cross-team contribution internally) was hard to impossible. There was no (or very limited) metadata available for things like a shared avatar or display name.
We had enough time to do these things, but we didn't. The team accomplished something really amazing, but it wasn't enough, and most importantly, putting more effort into what already existed was not going to work. This idea that Mozilla can just turn around and throw effort at Persona and make it win now is, IMO, wrong.
Identity needs more experimentation, that much is certain. But harping bringing back Persona in particular is beating a dead horse. We need a successor or a new project.
[1] Not only did this make Persona look incredibly sketchy without a lot of priming users, it had a major privacy issue of leaking your identity provider and relying party to Mozilla via a centralized iframe we host. A mailing list thread among the Persona devs and community failed to find a solution to this.