Microsoft’s PlayXBLA blog is teasing a Halo/Minecraft crossover that will likely take the form of a new Mash-Up Pack (like the previously released ones based on Mass Effect and Skyrim):
We don’t have specific details just yet, but we can confirm that Halo is coming to Minecraft. Details soon.
If you can’t wait to put Master Chief into Minecraft, don’t forget that a Master Chief Skin was released as part of Skin Pack 1 back in July 2012.