You can use downward momentum to get pretty high back up in altitude, but yes you can't "fly up". This is what I meant about being able to be teleported by going into a lower ring and and coming out of one much higher elsewhere (or one of the other methods I mentioned, probably would be best to be visual).
Oh, that totally is flying up. You definitely know much more about it than me :p, I thought it was like a glider, can only go down, but can choose to go slow or fast.
Using a punch 2 bow, if you time the arrow correctly, you can hit yourself mid flight and that boosts you upwards. In single players survival, I used a punch 2, infinity 1 bow to jump off a ledge at y=200 and get up to y=870 before the bow broke. This method could be implemented in the later levels because its harder to do, just give a high level of resistance to the player along with a bow with the unbreakable data tag. Also full support for this thread :P Love the concept!
I feel as if lag would play a huge role in this, for those whom don't connect too well to the server, or, people from outside of the US. We'll see how Tanner develops this, hopefully is happens because it's a great idea.