Within an Interview with the online gamemagazine gamedaily.com, Blizzard’s vice president of game design Rob Pardo, implies that “a new Warcraft RTS will be “one of the ideas on the table after StarCraft 2 ships”.
The complete Statement, applying  to Warcraft 4:

“Yeah, of course there’s a chance,” he confirmed. “The way that we develop things, each […]