First of all, Halo MMC is amazing. From the menus and layout, to remastered graphics to new playlists...if there ever was a definitive edition of any game, this is it.
However I can't help but feel like something is missing...and that something being Halo Reach and ODST! I know these don't really fit in with the Master Chief story but they are awesome games in their own right.
I don't think it would be too far of a strech to imagine DLC ($$) down the road that adds these 2 games to the Halo MMC collection. Perhaps even a standalone game that contains Halo Wars, ODST and Reach and somehow integrates in to one seamless Halo hub with the MMC...
All I know is that I want all Halo games accessible through one hub and interface. Make it happen Microsoft!