Things can always change, but I can see three motivations for a move like that:
1. Able to play QB guaranteed, which it sounds like Luke really wants.
2. Able to play for his Dad.
3. Not having to sit a year transferring versus transferring to another D1 school.
This guy mentioned that the staff had talked about it, take that for whatever it's worth. This could simply be offseason/new coach talk but I'm simply relaying what I heard.
If Smothers is good, and Martinez has 2 years left, then the QB avenue very well could dry up for McCaffrey. Injuries can always happen of course, but I don't imagine a scenario where Martinez doesn't start this year without an injury, so this will be intriguing none the less.