OR does he actually become the Earth Aspect like he pulled off in the books for a short time?

"walk the earth?"

So Thall's decided to be a bum?

When did he make this decision? When he was sitting there eating a muffin?

*coughBolvarFordragoncough*

I think Thrall will definitely remain a neutral character from here on out, he seems to be chosen by the rest of the Aspects to do the job Neltharion failed at and be the guardian of the earth. Thrall isn't an aspect but he is the effective replacement for one, he's the new Earth-Warder.

Even if he wanted to go kick Garrosh's ass out, which I'm sure he does to a degree, his new responsibilities will prevent him from doing that.

Oh, come now. Thrall "pulled this off" because it was in the script. Alliance could have easily done the same, had they been given the chance to.

Well, Metzen did say he would be Warchief again, but this won't happen yet. The only one idiotic enough to launch an attack on Theramore is Garrosh, so we will have to "enjoy" the little Hellscream at least throughout the whole new x-pac and maybe then, Thrall will kick his ass and come back. I still wonder what he will be up to when Theramore gets attacked, I don't expect him to sit there just watching the peace treaty go to hell.. it's gonna be really interesting :D

Just as an addendum Thrall is confirmed as the new Earth-Warder in this tooltip, an ability he casts on the tanks in the Ultraxion fight: http://www.wowhead.com/spell=106218

Worth noting that Ultraxion is the first boss after re-empowering the Dragon Soul at the Eye of Eternity, so that's probably where Thrall is chosen.

Thrall is not an Aspect, he's guarding the position. Wrathion is the Earth Aspect.

Wrathion becomes the Aspect of Earth - the black dragon who guides the legendary dagger questline - I think by default since there are no other black dragons around.

As someone observed in yesterday's Queue, there hasn't been any Earth Warding done for about 10,000 years, since Neltharion started neglecting his responsibilities. I suspect Thrall is Earth Warder in a temporary capacity, as one is required for the Dragon Soul to activate. He's not going to keep the position - although Wrathion doesn't seem keen on the job either, for now.

For the dudes claiming Wrathion will be the new Earth Warder, I see no evidence of that in the legendary questline. He's more like a mafia kingpin out to make himself "head of the family." Plus there was quite literally nothing in there about him becoming an aspect of anything, it seemed like he is just plotting his own rise to power. Just because he's the only black dragon, it doesn't necessarily mean that a black dragon will become the new earth warder (or that anyone will become another earth warder).