So, from what we've seen in the ptr, there's nothing really special about Wrathion's plan.
He sends us to the timeless isle to 'time lock' our cloaks and make them more powerful. Okay, that's neat, we get super powerful cloaks. I guess a weapon for every class and spec would have been a bit much. I can live with this though I hope there's a cosmetic reward like the dagger wings and dragonwrath mount. But regardless, we complete our cloaks and he sends us off to kill Garrosh.
At what point did we need Wrathion though? Sure, he gives us some cook cloaks and gems. But the story never really feels like his plan is having a realm impact on the present story. In the end his 'judgement' is 'go kill Garrosh to end the war.' That's great and all, but the Horde turned against Garrosh without his involvement, and he wasn't involved in SI 7 making contact with Vol'jin to make a truce against Garrosh. And in the end, his big plan is 'go kill Garrosh,' that thing we're going to do anyway?
There may be more to this that just isn't in the ptr yet, but that's all the quests and dialogue suggest.
So what the player character gets out of working with Wrathion:
A cool gem for weapons that are outdated now.
A gem socket for weapons.
A cool meta gem.
A kick ass cloak.
But what did Wrathion get?
1. A bunch of ancient mogu secrets.
2. A legendary weapon we help forge for HIM to keep. If I recall correctly he carries it around after the quest is done and even fights you with it if you do Xuen's trial.
3. A bunch of valuable titan knowledge he gets after eating Lei Shen's heart. Knowledge we only get cryptic slivers of.
In the end, it doesn't really feel like we needed Wrathion, and I think he benefited from us more than we did from him, considering the war he sought out to end is coming to its own conclusion without him really doing anything. In the end this quest line is really just about us getting him stuff in exchange for him giving us stuff, and when his big plan to end the war comes along it's the same thing we'd be doing anyway. Either Wrathion played us, or this is kind of disappointing. It feels more like setup for a later storyline than a story related to the current one.
I do love Tong's speech at the end of it though, his audio is awesome.