As with any rule there's pros and cons. But frankly with this rule I don't see many pros. I agree with Wade in that it's basically a PR move by the NFL making them look serious about head injuries.
My problem is the bit about the play being dead. There is definitely going to be a circumstance where this rule becomes controversial. For instance on James Jones play he had a clear path into the end zone once his helmet came off, but the play would have stopped there. Or more controversial, say it's a 3rd-and-eight, ball carrier takes a dump pass and gets hit, shakes it off but loses his helmet. There was easily enough room for him to get the first down, but the play is blown dead there because of the helmet, fourth down. It's bogus.
Plus why only the ball carrier? If someone else loses a helmet the play still goes on? What a linebacker lost his helmet and he swoops in to make a tackle. That's pretty damn dangerous isn't it? Or anyone on the line losing their helmets, they battle the whole frickin' play.
What the NFL really should do is work their best on making helmets that don't come off lol.
Of course, I can see coaches absolutely stressing to their players to check their helmets in between every play to make sure they won't pop off. Although, that could end up becoming an unnecessary distraction for the players.