Jul 24th 2010 6:10AM I haven't played horde that much (and Forsaken none) but I think I understand Sylvanas' motives here. Her goal is to give the Forsaken a place on Azeroth, and Lordaeron (as their native land before the plague struck) is her first choise. Now, because the Forsaken cannot reproduce themselves their forces will eventually weaken and as a result of that they will lose territories to the alliance. The only way for Sylvanas to ensure that the Forsaken have a strong presence in Lordaeron is to use the Val'kyr... From the point of Garrosh I can see why this brings tention to the relations between him and Sylvanas, after all I don't think he wants to see her grow too powerful. From what I understand, the common goal between the orcs and the forsaken have been to fight the scourge, and now when the Lich King has been defeated, that reason for an alliance is gone. What remains is - at best - a common hate for the humans. As hinted in Cataclysm, that the conflict between Horde and Alliance will grow hotter again, that might be enough to keep their alliance intact. For now.
To speculate wildly into the future, it's interesting to see how the Argent Crusade will respond to this. Their goal has been to clear Lordaeron from the scourge and as they clearly recognise the Forsaken as a race of their own it could be a possibility that they will consider the land liberated and that the Forsaken is its righful owner. In doing so their reputation with the Alliance would drop dramatically and if Garrosh decides to stage a coup d'etat to overthrow Sylvanas, or even declare a war to have her replaced, that could in a distant future lead to an alliance between the Argent Crusade and the Forsaken. Imagine both Garrosh and Wrynn going to a full-on war versus the Forsaken, over basically the Forsaken's right to exist. Given the similarities of situation between Ebon Hold and the Forsaken, it is not unlikely that the Ebon Hold would join the new alliance in order to secure Lordaeron and the rights of the Forsaken. Such a future could also mean that the Scarlet Crusade recieves heavy support from the Alliance in order to wage a guerilla war in Lordaeron, "behind enemy lines". And who knows, maybe Tirion Fordrings old pal from the north, the new Lich King (depending on the degree of demonic influences there...) decides to send aid... I can see the expansion following Cataclysm: "The Return of the Lich King" ^^
Actually, not too unlikely, given Blizzard's new strategy of making the world more dynamic. World is changing, new races joining alliances, old races leaving alliances, new alliances forming... Would be pretty interesting to see, in my opinion.