That doesn't really do anything meaningful for the franchise. Story wise, it'd be a crap rehash of Reach but with ODSTs, and we've already explored Reach. The first ODST got away with the location of New Mombasa because players only spent a couple levels in Halo 2 there, whereas ODST stayed there the whole game.
Reach 2 would be pointless as the story and characters all have an end, with no hint or real reason for a sequel.
ODST 2 could work, but it can't exactly be the same squad from the original, and would be better off in a new locale players haven't seen in game, such as Venezia, urban Harvest, Sydney, Cleveland, New Pheonix, Balaho, and such.