Within the freshest Starcraft 2 panel from BlizzCon 2008 Blizzard proclaims, that Starcraft 2 will be expanded into a trilogy. Furthermore Blizzard verifies, that Warcraft 4 will be released with the same principle.
Blizzard Co-founder Frank Pearce on videogaming247.com
“If there’s a team that’s passionate about doing another WarCraft RTS, then that’s definitely something we would consider,”
“It’s […]

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 […]