The domain names Haloremix.com and Halo4remix.com have been registered by a company called Roundhouse who deal with social media advertising for Microsoft. They've previously done Facebook projects for Dance Central, Halo Reach and Call of Duty.
We do know that there will be a disc in the Halo 4 Soundtrack album containing Halo 4 music remixed by various artists, so this could be related to that. Of course it could also be something totally different, I'll bring you more news when I have it.
- Cowboy Out.
Thanks to ForceImpackt for sending me the story.