Since we won't be able to fly in the old areas.....

[MilesSaintboroguh]

This simply isn't true.

There are no invisible boundaries in the new areas except for the actual edge of the map. There's nothing about the old maps that would need to be redesigned. They'd simply have to code the Z axis movement in.

I don't think it's that simple. 2.0 maps doesn't have flying, thus the map designers don't have to worry about making assets or other objects in places the player will never see. Now if you give them the ability to fly, the devs would have to redesign a lot of maps so that we don't see ugly blank spaces way up high.