Halo 3 Supplemental - what is it?

Not sure where this is all going... but it's interesting. Falagard dropped by with a report of a conversation that took place on the NeoGAF forums - the gist is that Alan Tudyk, an actor who did voice work for Halo 3, reported at Gencon (a gaming convention in Australia that took place a week or so ago, July 3-6) that he and Nathan Fillion and Adam Baldwin had recently "recorded voices for a Halo 3 supplemental" - could this be the Halo "Blue" referred to recently by Joystiq? It sure sounds like Bungie's working on SOMETHING Halo-related...(Louis Wu 17:11:19 +0000)