We'll see. In the wake of increased security measures post-9/11, the 9/11 M.O. may have given way to more opportunistic tactics, e.g., sabotage, ground-to-air attack etc. A big plane going down in a crowded city suburb still packs a wallop and makes a statement even if not fully fueled.
If it is not terrorist-related, the timing and venue are nevertheless astonishing and especially unfortunate. This will be another savage blow to American Airlines and the airline industry.