Just replace the motherboard with a GPU board with cooling solution on the bottom, and CPU socket on top along with all other connectors. Make them in 2 standard heights so cases can be standardized. The boards will have NO slots since the board IS the video card. This is of course only slightly serious, I prefer to use AMD chips with integrated GPUs and SFF. But for those that care about GPU capability lets just change the priority of the components and build the PC on top of the graphics solution.