If you've stopped by the Dark Portal in the past several hours, you may have noticed some changes. Alliance and Horde forces have begun to push the Iron Horde back closer to the portal. Khadgar, along with Thrall and Maraad, have taken up station in front of the portal.
When the clock strikes 12 a.m. PST (North America) or 12 a.m. CET (Europe), you'll be prompted to visit Khadgar in the Blasted Lands to start your journey into Draenor. In past expansions, the NPC which gave you the first quest tended to be a bottleneck of sorts. Usually it was because of some unsavory individuals who decided to sit on their oversized mammoth mounts right on top of said NPC.
You'll be happy to know that Khadgar has collisions around him, meaning no one can sit directly on top of him. And best of all, mounting is disallowed in a 15 yard radius around Khadgar. Sorry to disappoint you, mammoth trolls.