Listen to the recent podcast that 343i has posted onto the front page. At 34:00 minutes exactly, into the podcast, they discuss that they have just recently shipped something very big, something huge, something heavy. Could this be the Title Update that we have been waiting for? What else could they have been working on? A TU would be a very heavy file in order to patch Reach and maybe this is what they were talking about.
A little before the 34 minute mark you can also find out what to expect from HaloFest and it would be an amazing time to announce the TU!