There are appropriate holes for all the currently listed and future compatible chassis. Standoff heights vary from case to case, but they are not trying to put the cables behind the motherboard, but behind the motherboard tray as ususal.
Plenty of video out there from the various electronics and computer conventions where the prototypes of these made appearances, if you are curious.
Today with as big as GPUs are getting, you lose several slots. If the GPU x16 slot was on the back and 90 degrees like you can achieve in Mini-ITX boards with a riser, you could keep all the other slots on the front accessible. Also allows you to separate GPU and CPU cooling. You could at that point also make the front side slots 90 degrees and reduce over case width. Not much of a market, but I still think it would be interesting.