the original OP on that Chinese forum is a high-rank moderator of that forum, he knows a few things about the new expansion for he has some relation with the agency company of WOW in China and even with Blizzard.
He leaked some information 2 years ago before WOD, it turned out that he indeed knew but had to make it obscure because he had to keep it confidential to some extent, since it was still a relatively long time before WOD was officially disclosed. But this time there are just a few days before gamescon so he decide to tell more truth but still plays some word games.
There is in fact another post on the new expansion by another moderator of that forum, which is more straight forward, but this post didn't last long because Netease( the agency company of CWOW) demanded the forum to delete. The information leaked by these two posts are merely the same.
The new class is very possibly called "demon hunter", but might be the combination of the demon hunters in D3 and in WOW in the way of game play( which means it may has nothing to do with the D3 demon hunter in the respect of game storyline but can do ranged dps).
In fact there a post several days ago on this forum by a guy who gave some information on WOD 2 years ago, the post is banned but its major content is similar to the two posts on the Chinese forum.
All the three posts indicated that the new expansion has something to do with Guldan going to the tomb of sargeras, so which means having something to do with islands and nagas.
and the new class, it may has 2 specs of dps which I guess at least one is ranged, the 3rd some guess may be healing( the post on MMO-Champion indicated the new class is call shadow walker that has 2 specs of ranged dps and 1 of healing which is much like the shadow hunter in Warcraft)
something will happen to the high-level persons in both Horde and Alliance, the moderator who wrote one of the post on the chinese forum said "revolution", many guess that the chief of the Horde will change again, might be Voljin somehow step down.
and trolls will again play a important part in the new expansion
the above is just my personal comprehension on informations leaked so far, I myself is a long-time user of that Chinese forum, sorry for my poor English, it's nearly wee hours in China so I have to type in quickly and then get some sleep