ODST is more or less, a tide over. It's made to expand the Halo Universe's story, and deliver it in a new way. The FireFight portion will keep people busy and happy for a while, and the new achievements should be fun.
However, most of their effort and time is going into Reach to make it into a freaking sweet game. There would be no point in making a completely new matchmaking experience if people were going to move onto Reach in a year. I see FireFight as a (slight) beta (ish thing), if it goes well, Bungie might include it in Reach. So far, so good.
Thats why I don't think Bungie would include a new matchmaking experience and why I personally don't think that would be a good idea.
Oh, and... Wall 'O' Text FTW!
~Hunter