It sounds interesting, but I'm not sure how it would work. I guess if you had a mix of QBs with different strengths (e.g. one that is better at throwing long, one that is better with quick-release short passes, and one that was better scrambling/running and evading the blitz) it would give you options. The problem I see is that having specialty QBs might tip off the defending team what you were going to do. You bring in a guy who can throw long - you're probably going to go long. You bring in a guy who can run with the ball, maybe you're going to run. I guess you could use the move to decoy the defense into thinking you were going to pass - but then run - etc.
I would question the pay and quality angle to this. You’d basically have one four-star quarterback, and three two-star quarterbacks. There are certain clubs where this might work, but you’d have to really think and build intensive strategies over this whole idea. And it wouldn’t surprise if the teams ask to expand the ceiling numbers by two or three more players to make this work.
I'm thinking of short-yardage scenarios, and perhaps even on two-point conversions.