Pretty sure the team doing Starcraft II is the same team that did all the warcraft games.
So until Heart of the Swarm and Legacy of the void hit the markets there is no hope.
But I'm pretty sure warcraft 4 will come after they are done with the starcraft II expansions.
I mean there is so so so so so so much lore in warcraft and you can always just write more.
Warcraft 4 will come some day.