Model hobbyist and Gundam fan Angelo Guibone's custom Master Chief Zaku crossover not only appeals to two camps, its will probably appear in a proposal for Microsoft Tecmo Koei's Halo: Dynasty Warriors: Gundam: Combat Evolved at some point.
In more serious matters - this hasn't happened yet? I see more than one Master Chief custom Transformer out there on the internet, but not another Spartan Gundam. That can't be right, can it? More pics of the MC01-Zaku at Guibone's blog.