An AWB is only one possible scenario, and IMO, will depend on how this is all spun by the media. We don't have all the facts yet, but so far what I've heard is one .223 rifle, two 9MM pistols, and "over 100 rounds fired". Among other things this could be:
1) A new AWB
2) Magazine restrictions
3) Ammunition restrictions (type, quantity, paperwork)
If we find that most of the shooting was done with the pistols, or that he reloaded magazines, or that he had "X' amount of ammunition on him or nearby or at his home, any of these could trump an AWB as a possible scenario if the media spins them up.
Personally I am, and have been since the Colorado thing, much more worried about ammunition restrictions or monitoring. Think of all the people that consider 100 rounds of ammunition to be a crazy big quantity. Restricting or reporting even a few hundred rounds of ammo would be an easy sell to the average American. I wouldn't be surprised to see paperwork for ANY amount of ammo get passed.