Sal Maiorano was saying earlier this week that in the 4th qtr when the Bills are within one score of taking the lead; that Tyrod has a 40% completion rate and a QB rating of 50. I dont know about EJ (he might be OK) but Tyrod has been unable to light it up when the teams back is against the wall. It likely isnt exclusively his fault. Play calling, route running, injuries etc. They all play a role.
The problem with the OP's idea is there is only so much practice time and these 2 QB's splitting reps with the #1's would likely dilute their readiness for each opponent. Additionally, you also take the risk of creating controversy, locker room taking sides and a media that will throw nitrous on the fire.
But, I wont pile on....... even though its the in-thing to do on this forum. The OP is simply asking a question. Nothing wrong with that.
EDIT: very much agree with the quote below..I hate to say.....