Unlike the horrible aggro symbols this sounds actually quite handy. Now if people could just use this as basis for attacking or avoiding enemies maybe they could take out the bake-sale symbols?
It's not visible anymore. At least not the whole time. When you select a mob you'll see either a red (for aggro) or a green dot (non aggro) behind the rank number of the mob.
NM rank is still "??" but the mob info also features the red and green dot.
I like this change and the fact that you can turn all of this on or off.