Okay, I know that Demoralizing Roar is being buffed so that it'll match the warrior's version at the highest level. But here's the thing - it doesn't at level 70. Nothing's changing about demoralizing roar at level 70, so it will still provide only a 220 AP drop untalented and 336 talented.
This is compared to the 300 AP drop from demoralizing shout that gets buffed to 420 talented.
Yes, it'll be worth it when you hit 80 if you're going to be the AP debuff guy. It'll be just as good as a warrior's version. But right now the only reason you should get feral aggression is if you don't have any warrior in your raid at all or for whatever reason can't have a warrior debuff the mob.