Watch the WoW Q&A, notice how much GC is trolling with his "xxx confirmed" running joke, and you'll understand..
You'll realize that knowing what you're talking about actually helps in most conversations
antagonist =! End boss. The other leak that predicted most of the features of WoD stated that "there is something behind Hellscream
S", which Metzen confirmed during Blizzcon.
Blizzard devs aren't that silly, even they can see it would feel wrong to have another "simple orc" as an Xpac endboss again.
As for the true endboss, if they did say that it won't be a demon either, I guess it'll be either a Draenor Old God, or some titan watcher since we should discover titans visited draenor in the distant past, but "peaced out quickly".. Maybe Draenor was "parasited" by Old Gods too, and the titans didn't manage to contain them as well as they did on Azeroth ? (seeing who many we already met, it may not be that hard to imagine...
)