Yes, such a scheme unavoidably requires trust in the mintettes.  Laurie makes this clear in his paper.

I'm looking for a centralized authentication system with flexible federation/syndication, because I think it should be possible to arrange things so that the authenticators could only cheat effectively by colluding on a large scale, and such an arrangement would increase the system's trustworthiness and robustness.  I don't have a clear picture of it, yet, but it may not need a secondary blockchain like you're assuming.