I disagree. Persona piggy backs on email system so it doesn't need a critical mass of users to be useful. Persona as a brand may not become widely recognizable

I disagree. Persona piggy backs on email system so it doesn't need a critical mass of users to be useful. Persona as a brand may not become widely recognizable with limited involvement from Mozilla, but some people argued from a beginning that it was a mistake that Mozilla tried to create a recognizable brand. The team succeeded at creating smooth email verification system. As long as Mozilla keeps servers running, quickly solves security issues and accepts patches with improvements from community, Persona will be used. I strongly believe it will organically grow and eventually will become a crucial part of the open web.