Sadly… the rumor has now been shot down, for now that is.
The rumor started when many new games were discovered in Steams database of potential new titles, among the list were Halo CE, Halo 2, and Halo 3. There were even Steam community pages for Halo 2 and Halo 3 giving the Halo fans some hope.
Sadly, Microsoft quickly denied the rumors in a response given to Kotaku. It may be a far fetched idea, but if any updates come up I’ll keep you informed.
– Chief Landless