I know a lot of Allys feel very passionate about the prospect of reclaiming Gilneas. If that were to happen and the Alliance gains a capital city, would my fellow Horde be cool with us getting Blackrock Mountain?
Blackrock Mountain was the headquarters for the Horde during the second war and the Blackrock Clan still has a sizable presence there. Blizz could re-acclimate the Blackrocks in to the Horde in a similar way they did with the Dragonmaw. Have an uprising from within against the Fel leaders of the clan, have the Horde come in and dispose of the old guard and establish a city.