Since Windows 8 has massive amounts of DRM built-in, why not just set a spec for branded OEM provided hardware? Microsoft does this with phones and used to do it with tabets. In the end, what is different about xbox verses something like a Windows 8 RT device? Things that might go on the certification might look like this:

* Boots under 10 seconds
* Conforms to DX11
* Scores at level X for benchmark Y
* No crapware allowed
* Is no louder than Z decibles, under stress 
* Supports controller spec
* Has at least one HDMI out