It's definitely related to WoW. 2 reasons.
Hearthstone is a FTP game which is still in Beta. Why would they need an 'expansion' for a game that is already FTP? They would just push whatever new content there is to the active client like a patch.
Draenor is apart of Warcraft lore and thus, since Hearthstone has been ruled out and Heroes of the Storm is the new name of Blizz All-Stars, that only leaves WoW. Since it's being copyrighted everywhere just days before Blizzcon just like what happened with Mists of Pandaria, all signs point to WoW.
And don't hold your breath for Warcraft 4. If it exists, it's likely 2-3 years from being complete.