I remember before ESO was released, there was talk of some kind of false Tribunal member showing up in-game. As I haven't progressed that far in the game, and I haven't heard anything about it since, I was wondering if there's any new lorebooks/dialogue/screenshots of this guy, or was the quest cut before release?

I migth be wrong as I don't play ESO and most of my knowledge of it comes from reading and watching films but I think there is a questline were some woman has a beef with Almalexia and tries to return Dunmer to Daedra worship and this is what they mean by Trinunal pretender.

The common era is too early for the girl to be Peakstar, but maybe she's another failed incarnate. Ane Teria faithfully served the Tribunal in their golden age and enlighted Temple ecclesia, when she introduced to them the Nerevarine prophecies. I think that Temple censors and inquisitors construed her as a daedric rebel.