I see football evolving into far more of a skill-first sport in the future. I don't think the physical element will ever be entirely removed, but I do think that penalties like unnecessary roughness will continue to be expanded in increasing efforts to mitigate injury. A point may arrive where football players resemble basketball players much more than they do now, that the battle of the line of scrimmage will become more about zone denial vs zone penetration instead of power against power, and that penalties will prevent the big power footballer from being as effective as he is right now.
I think it's very possible to play a game of professional football without quite the level of aggression and violence the game's played with today.
I also think, and this is my honest prediction, that it's going to take some poor guy DYING on the field to force the NFL to go in that skilled direction instead of the "traditional" emphasis on power football. For as long as the sport is governed by old men, it will face the future only reluctantly and only when it has no choice.