Honestly, if they implement it right, I don't see a problem with them testing out no-flying for a while. Not having flying didn't feel like a drag at all in Mists of Pandaria while leveling. That's while its flight paths are complete horse shit. If they finally stopped forcing scenic flight routes down our throat (or at least make them optional), travel time wouldn't be that much longer, it would also throw some gold out of the economy. If they also make ore/herb nodes spawn closer to eachother, like in Vanilla zones (where you often see 5+ nodes on a single minimap), it wouldn't make gathering a drag either, because everything would be more concentrated. Adding a flight path to every single town (like in MoP) and to raid instances would also help.
They would also have to make the running animation of a lot of flying mounts a whole lot better, though.
Long story short: Blizzard could pull it off, removing flight from the game, but it would require quite a bit of work. It seems they really want to do it, though, and if they do it right, it could be really awesome.