According to Wholly, this quest is locked behind the prerequisites. Through the Dark Portal [9407] or Warcheif's Command: Outland [28705] but this is no longer the case.

At reaching level 60, a new character is given the quest: Adventure Calls [49860] which asks the player make a choice between Northrend, or Outland as their next task. A Special Duty Assigment scroll is provided for this.

If the player selects Outland, they are given the quest: To Outland! [41896] which grants access to the quest Arrival in Outland. I imagine there will be a similar case for Northrend starter zones.

Just a head's up, but the next quest is given at lvl 80, called Wars on Two Fronts [49846] and offers a choice between Cataclysm content and Pandaria. I'm guessing this may invalidate other breadcrumbs into these areas, but I haven't checked yet - finishing off the BC zone I was in

Okies, so I'm done with that zone, and opened the scroll. Completing the quest opened up a new quest: To Pandaria! [49852] which sends you to Grommosh Hold where you get the Mists of Pandaria cut-scence and then next in the chain: All Aboard! [31853] likely invalidating Art of War [29611]

Well, that's weird. Apparently it's bugged and accepting All Aboard! [31853] makes Art of War! pop up so you have to watch the cut-scene again lol. I guess they will fix that eventually