Imo, with right patch schedule of course, X.3 should always be true filler, some completely side story that takes place somewhere in old Azeroth (any zone, not just EK/Kalimdor), with size similar to 8.3. This way story would conclude in X.2 and new expac reveal wouldn't spoil anything.
Ironically, you could make strong case that 8.3 was exactly that. But you know what I mean, something more like Mechagon than N'zoth.