No doubt Turalyon might stir up some drama. He recently said that he seeks to reclaim other former holdings of the Alliance of Lordaeron, in the wake of the Alliance Reclamation of Stromgarde. Depending on how Voss/Calia/Whoever-leads-the-Zombies respond, there might be some clashes between the Forsaken and the Alliance over control of these former holdings.
But I'm not expecting actual full-blown war/Fifth War, but there might be a few new questlines or a new battleground simply centred around these border clashes between the Forsaken and the Alliance.