I'd love it if they made a Halo ODST style expansion. They could tell Jun and Halsey's story from the end of the Reach game. What I'd really love is if they did something based on the Spirit of Fire after Wars. That would fit with Halo 4's lost ship theme.
My Setup: http://tinyurl.com/d395sf6 PSN/XBL/Steam: Willavom