I found a new board-id (Mac-65CE76090165799A) in AppleGraphicsDevicePolicy.kext/Context/Info.plist (Beta OS X 10.10.3) of a yet to be released new Mac with a Retina 5K display, but I have no idea what kind of Mac this would be. Perhaps one with a new Broadwell processor? Again. I have no idea. Really.
Edit: It uses the same Config2 and EDID data of the iMac’s with board-id Mac-42FD25EABCABB274 and Mac-FA842E06C61E91C5 (both with Retina 5K display) so it looks like another iMac.