Due to game mechanics it's impossible of course, but perfect moment to march north is during siege of orgrimmar. Instead sending entire alliance millitary power to destroy Garrosh, Varian should let the horde bleed out and claim Arathi,Lordaeron and Gilneas. And don't tell me Forsaken are so powerfull, they don't have a chance against Humans,Dwarfs,Gnomes and Worgens (espiecially with gnomes/dwarfs tech). I'm still wonder what will Alliance get after Siege of Orgrimmar ?. It's also perfect opportunity for night Elves to secure Ashenvale and Azshara while Horde races will be fight each-other.