You are actually reducing the risk to any given QB because he spends less time on the field but the total risk for injury at the position is the same as playing a single QB +/- the mitigating factors in such a system.
Factors like fatigue probably reduces risk and lack of player familiarity probably increases risk. Player personality, physical condition and such also figure in to it.
In the end I would guess that all of the little mitigating factors probably end up cancelling each other out and you end up with the same risk to the QB as a single QB system.
This is no different than the rotation at running back, wide receiver or any other position on the field. The less time you spend on the field, the less likely you are going to get injured.
There is just some stigma about rotating players at certain positions, mainly QB and Kicker.
The real differences between the NFL and college ball in this case are the size of the teams and the dollar investment in the players. In the NFL you have less players available to rotate and QB's cost a lot of $$. Those are pretty good reasons not to rotate QBs in real terms. All scholarship players essentially cost the same in in college ball and you 60% larger teams. I guess old habits and myths die hard.
I have stated in other posts that I think KF will never go to a two QB system based on simple rotation. I do believe he would use a second QB situationally, possibly in some sort of "quick strike" package, as well for end of game clean up duties (if we ever see that again).
The JC/RS situation was described by KF as a "QB competition". He seems to think this competition is over. At his age you would think he would have figured out the competition is never over.
