I highly doubt they will completely remove flying from the entire expansion, for a few reasons. First, there would be a huge backlash that would result in a lot of lost subs. And we're talking about more than just a few. A storm of protest hit the forums when they announced that flying wouldn't be instantly available at max level already. Secondly, they continue to design and sell flying mounts through the blizzard store. Not only would restricting people to the ground indefinitely be a slap in the face to those who purchased the mounts they already have, sales would drop to 0 on future purchases and new flying mounts would be far less likely to sell. I don't believe they will take the huge financial losses that would come from those two things. And I think I'd probably stop playing if they indefinitely took flying out, not because I need flying so much, but more because I would consider it a complete middle finger as a player.