If Jason is still running the show then the clues to who will be considered for the backup QB center around these factors:
1. Do they have experience in the Coryell offense trained preferably by Norv or Linehan? Bob Bratkowski, Cam Cameron, Brian Schottenheimer, and especially Hue Jackson (because of the current success of the Bengals offense) are also considered worthy mentors of Jason's interest in a player.
2. Did they attend a school that has experience in distance and timing routes?
3. Do they or did they attend a high character school like Baylor?
My guess is that the QBs with most of those qualities would be RG3, Taylor Hernike, or AJ McCarron (would have to be a very valuable trade)
But if Jerry saw that Weeden and Cassel were erroneously trusted with the keys to the Ferrari based on Jason's "Norvs stamp of approval" and Jerry is reconsidering the Garrett's (Judd and Jason and whatever influence Jim still has) talent standards (as evidenced by this season's wave of non-RKG players and the failure of Garrett players such as Streets and T.Williams), he might seek the backup QB on his own...like Manziel or someone from his favorite schools like Oklahoma, Arkansas, A&M, or Boise St.
Ultimately, if Jason is still coaching and is unyielding that his "system" is the absolute monarchy of the offensive part of the team, then no matter who the QB is, aside from one who can scramble well, the speed and talent around Dez has to improve or the QBs in Jason's system will continue to encounter the failure that Romo, Weeden and Cassel did this year. Streets runs a 4.55 and gets knocked out of his patterns and Terrance Williams, plays scared, runs only a 4.5 and doesn't catch the ball above his chin. Most successful Coryell offenses have WRs who run under 4.4 (see the Manning Colts and Warner Rams). Dallas has WRs who would be great at high percentage offenses like the WCO: tall, good RAC and prefer close high percentage passes.
To be sure, look at this basic description from Wikipedia of the players required for Jason's Coryell offense contrasted with a Walsh WCO:
"The Coryell offense attacked vertically through
seams, while the West Coast offense moved laterally as much as vertically through angles on
curl and
slant routes.
[24] The Coryell offense had lower completion percentages than the West Coast offense, but the returns were greater on a successful play. "The Coryell offense required more talented players, a passer who could get the ball there, and men who can really run—a lot of them," said Walsh.
[25] He said the West Coast offense was developed out of necessity to operate with less talented players. He noted, "[Coryell] already had the talent and used it brilliantly."
[25]