There is no next expansion. Why? Because Northrend isn't even on that map. The Horde is using a map that lacks Northrend to discuss an assault on Northrend. I think I have some idea of how their conversation really went down at their war council. Check it out behind the cut below.
"What do we know of this... Northrend?" Thrall asks, looking to Sylvanas.
"It is to the north," the Banshee Queen replies in deadpan, rolling an inky black arrow between her fingers while empty eyes peer at the map below like a hawk would to its prey. "Also, it is cold."
The Warchief returns his gaze to the leather parchment, brow furrowing in thought. "I see," he says, thick green finger tapping the stone table between them. "It is probably around here somewhere, then. I think our assault needs to wait until we can draw another squiggly circle here."
High Overlord Saurfang steps in beside Thrall and shifts the weight of the axe resting heavily upon his shoulder, leaning in to get a better view of the parchment. He clears his throat and speaks, voice low and rumbling within his chest. "Warchief, I think Northrend is more of a triangle."
Thrall nods slowly, coming to a grim realization. His voice comes quietly this time, "A triangle... This war may be more dangerous than any of us could have imagined." He looks up, straightening his shoulders and regaining his composure. "We need to think on this further! We should consult with Jaina Proudmoore before we-"
"Are you mad!? Are you a coward!?" Garrosh Hellscream, son of Grom, throws his arms in the air in fury. "We are the Horde! We have no need for maps! LOK'TAR OGAR!"
And then the Horde gets lost at sea and dies. The Lich King overruns the Alliance. The World of Warcraft ends. Good job, guys. You blew it.
Thanks a lot.
Edit: The picture of the map was originally upside down, so I flipped it vertically and forgot to flip it horizontally before posting it. I've fixed that, so now Kalimdor and the Eastern Kingdoms are on the right sides. Northrend still isn't there, though.