Probable factions in Wrath of the Lich King

Jikiyami from Kul'tiras dropped a tip asking us about all the different factions that might be in the Wrath of the Lich King expansion when it comes out. Unfortunately, Blizzard hasn't completed design on most of Northrend, so I'd bet that the actual list of factions isn't really determined yet. But that won't stop us from speculating who you might be working for from level 70-80.

There will most likely be Horde and Alliance starting factions, just like Honor Hold and Thrallmar. For Horde, Forsaken seem to be taking the spotlight (according to what we saw in the playthrough), so an "Apothecaries' Guild" faction might be up there. For Alliance, I'm betting the Dwarves will lead, so an "Explorer's League" type of group might be a good guess.
Dalaran will be up there, of course, so we'll either see the Violet Citadel make a return, or another Mage-based faction.
The Tuskarr, a new race, are supposedly fighting against Naga trying to melt their grounds, so I bet we'll see a faction for them.
Lake Wintergrasp is a World PvP zone, so expect a Horde and Alliance faction for each side.
We know Gnomish flying machines will be available in the expansion, so I'd guess there's a Gnomish faction to rep up for in order to gain access to those.
In Dragonblight, the rumor is that Deathwing is setting up shop, so there may be a new faction fighting against him.
And that same faction may be situated around the Nexus, an instance hub in which Malygos is running things. Then again, we've heard that Dalaran is fighting Malygos' campaign against magic, so this may overlap with the Mages there.
Jikiyami points out, rightfully, that supposedly some Nerubians are fighting against Arthas, so outside Azjol-Nerub we may find a faction ready to give us rep for fighting in there.
And finally, someone's got to lead the battle against Arthas and his Scourge, right? Blizzard seemed kind of opposed to this at BlizzCon, but I would be very, very disappointed if the Argent Dawn didn't have some role to play near Icecrown Citadel or the new Naxx.
Or maybe Arthas will have his own rep to grind-- how else would we get access to a Death Knight?
So there's about ten guesses at different factions right there. And who knows if older factions might show up-- since so many players are now allied with the Scryer or the Aldor, will they come back through the Portal and have a place in Northrend? Either way, there'll be no shortage of rep to grind in the cold north.