Getting into that ROM package is a bit tricky since their are new tools need for the new format, but progress is being made.
Case in point, user 'Fdo35' has found some images in the "oemavatar.cab" in IMGFS. Those images might be a mockup of the HTC Mondrian, specifically when the phone syncs with the Zune desktop software, ala Windows Mobile Device Center and it pulls up the image of the phone for that custom look. Or it may be just a dummy image.
Also found in the registry were references to the device not having a physical keyboard and a "4.3in WVGA Optrex" screen; similar stats to the HTC HD2 (but the rendering looks more like the original HTC HD). In addition, this ROM is possibly working off a "... QSD8650A/B (both are mentioned) chipset, which supports both CDMA and GSM, and is the only Snapdragon chipset which will get the new 1.3GHz Scorpion core"
So, what to make of all of this? Let you imaginations run wild or put your skeptics cap on (we advise the latter, but prefer the former). Hopefully more info will be coming forth on what exactly we're looking at.