The most interesting part of this to me is that they have a path, both in code and in process, to fallback to peer-to-peer if stuff breaks. That's pretty impressive.
Also interesting and impressive: Halo multiplayer fans have modded the original Xbox version of Halo to act as a dedicated server for Xbox LAN multiplayer[1] that serves the same architectural role as 343's UHS does for MCC online play.
The clients still talk to the official servers which run matchmaking and group up players together. The difference is whether the matchmaking servers tell all the players to connect to a dedicated gameserver or to connect to one of the players.
