https://wiki.mozilla.org/Identity/Persona_AAR
Both the team and some of the underlying technology are now at work on Firefox Accounts, which is a simpler (non-federated) system that will power the new Firefox Sync service, the Firefox Marketplace (for installable web apps on Firefox OS and other platforms), and other Mozilla services.
But it's open source :) we're still working on getting it there. The next release will dramatically scale back the API complexity, lock in the APIs and data formats, and pave the way for native browser extensions, self-hosted polyfills, etc.
Persona ain't going away so long as we're still relying on it.
For a more informed answer, you can ask the team directly in the mailing list or IRC channels listed at the bottom of https://developer.mozilla.org/en-US/Persona#Join_the_Identit...
[Edit: Or see callahad's reply in this thread.]