It would be really nice.
I'm tired of seeing the defense line up against my off-tackle run left (for example) with a blitzing LB or DT poised right there or in full-on run blitz but unable to call a run right or deep pass audible.
I get it matters not to the guys who just create playbooks and game plans and then click sim - but some of us actually love playing every down. Even if the QB via AI (or based off of say 4 pre-player selected plays in Strategy) would call audibles that would be something.
I'm assuming it's not in the game because the game has already calculated the play before I even click "play" (I'm essentially just watching a video)? It's the only reason I can think of as to why it's not included and if so that's a real shame.
It would also be nice to make substitutions on the fly too. I know there are the package options but again that's all done upfront and feels more for the guys that "click sim".