Well, to be fair, other teams are asking the same question (future starter/backup/waste) of Kaepernick, RG3, Weeden, Cousins, McCoy, Ponder, Cassel, Tannehill, Glennon, Cutler, Dalton, Foles, Manuel, Hoyer, Manziel, Geno Smith, Locker, Mettenberger, and Mallett. And I'm guessing the Giants will be questioning Eli Manning going forward as will be Jacksonville with Bortles. I wouldn't feel comfortable betting the ranch on Bortles and passing on Mariota or Winston. And the Saints might be wondering what exactly they have with Brees in the near future.
Just as Romo was not ready when he was a rookie we have to wait and see with Vaughn. We won't know until he sees live action. And that may be never if the Cowboys draft a Petty/Hundley or some other QB in the early rounds.