Was actually hoping to hear about this, too. Friend of mine bought the Legendary Villains: Vigilantes book for me because I wanted to play a Symbiote character and originally I was gonna wind up doing a kind of Wild Soul/Synthesist summoner multiclass deal, but after some googling found out that there was a whole class for them already.
After looking at the book, it says that the Vigilante Specialization is replaced, but I was wondering if they were forcibly locked into either Stalker or Avenger, or if they just don't get one at all. Hoping it's the former, because a lot of the talents that are exclusive to the specializations are really nice, especially the ones that are included in the book itself.