If I were a coach in a similar situation (two fairly close options with a slate of awful competition), I would alternate QB's every possession, and compare how they do in every situation (down and distance, field position, hash, etc.) Call every drive like it's a tied game. I'd already be doing this in practice, too. If one isn't clearly superior at every situation, play the QB that is superior in each particular situation.
This is obviously way oversimplified, but it is IMO the best approach to a 2QB scenario. I also like to think some version of this will take place (or is already).