That would make a three hour game five hours long. You start getting into network monies then. Long story short - won't happen, no matter how good the idea seems.
Personally I think the NFL at some point is going to start having rookies sign waivers for future injuries when they come into the league to avoid potential lawsuits. Something that might include a one time payout in the future if such-and-such injuries ever become prevalent to the player.