Remember when Quinn was signed and all the positives spoken about him (by Pete and John, others) were regarding his work ethic (both in the weight room and in the film room), not anything to do with actual football skill or performance as a QB?
I scoffed at the time (as I think many here did), but it strikes me that that might make for the ideal "shadow roster" QB (ie the 3rd QB when we only keep 2 on the 53 man roster). With Quinn, you can give him as many preseason reps as you can reasonably spare to get up to speed on the offense, then release him at final cut downs. You then rely on that vaunted work ethic and trust him to keep himself in game shape (physical and mental) while he's a free agent.
If injury strikes one of Russell or T-Jack, Quinn could step right into the #2 role, where a more talented or higher upside but lower work ethic QB might need a few weeks to play his way into shape.
I know there's been a lot of talk over the years over Pete and John's use of the so-called "shadow roster," but I hadn't seen anyone connect it to the Quinn signing.