Do you think that all content of old zones could and should be scaled? I.e., you'd get the same amount of experience in any zone (apart from starter areas and the newest high level zones), and the mobs scale to your level to provide a consistent challenge.
This would mean that Blizzard could put even more focus on the narrative, something they love doing these days, and less on creating a 'correct' leveling route. Story-branches in one zone could instantly lead to something else halfway across the globe, and incorporate all kinds of material in their plots without the constraints of having to use the traditionally correct zone next. It also means no more linear leveling of alts. So let's say you're leveling a human, that would mean you could do it in the following order for instance: Elwynn -> Arathi Highlands -> Nagrand -> Un'goro -> Southern Barrens -> Eastern Plaguelands -> Westfall -> Shadowmoon Valley -> Hyjal -> Grizzly Hills -> and so on.
You would choose your path and your experience; unused zones that you never see nowadays (like the latter zones Outland and Northrend and several low level zones); and every alt would be more fun to level up. I may throw up if I have to go Blasted Lands -> Hellfire Peninsula etc. one more time.
What say ye?