99% confident that its Casey's job to start the season, but the second QB will be given a real opportunity to unseat him if he outperforms Casey.
The fact that Diaco plans to use two QB's suggests it is Casey's job, Diaco's reasoning for 2 QB's was that the second QB offers a different skill set. I assume that means running the ball, from my observation Casey is the non runner of the group so he must be playing. Would you start the runner and bring in the non runner as a change of pace? Maybe but unlikely.
There have also been many other small hints that it is Casey's team. I'd be shocked and disappointed if he isn't leading the team into battle in two weeks.
Hopefully all three QB's stay with the program, we certainly need them. Boyle has NFL athletic potential, if he could learn to mimic Casey's mental agility he would be great. Stick with the program, learn and compete, then play on Sunday's.