They could port over the multiplayer if they wanted to, but they have already stated to not do so due to the fact that they didn't want to split the Halo multiplayer base into two games, especially since Halo 4 is coming out next year. So the guys who would have worked on that are either making the rest of Halo Anniversary look better or working on Halo 4 and making sure that's as good as it can be.
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