The more I think about it, the more I'm starting to agree with Steve. Most of the time, the 15 yards will result in a first down anyway. And the coach will certainly know that they're not getting a FD any more, so most of the griping about no first down is going to come from outside the fences.
I'm starting to think that the "stop participating in the play when your helmet comes off" and "leave the other guy alone when his helmet comes off" are going to be the ones that can be more problematic. I get the idea behind them, and I know those rules are just trickling down from NCAA, but I don't think it's realistic to tell Bubba the left tackle that if his helmet comes off, he has to stop and stand there instead of picking up the delayed blitzer.
(I'd still like to see DPI become the spot of the foul or 15 yards, whichever is less, plus AFD, but what I want is neither here nor there.)