I don't know what those kext imply, however, if that's point to a new display with build in eGPU. They only need the Device ID for the chip that will be installed inside the display, why including other chip's info? I still can't see why Apple want to provide general eGPU support.
Also, the eGPU inside the display only need to be a bridge to drive the 5K pixels, no need to provide any computational power. So, the lowest level chip that just enough to drive the pixels is good enough. Of course, even that's a low end chip, we still want to able to use that extra GPU power, but that's not the Apple's way.
If they decide that's the best way to make the 5K display, they will install a chip at there but we can never utilise it. Just like they put the "K" CPU inside the iMac but we can never ever OC it. Of course, they will still charge us accordingly + the Apple tax.
In both case, the problem points to the same issue, heat! the iMac obviously just barely can cool down the CPU. Even without OC, the iMac still rely on thermal throttling. So, there is no room to OC the "K" CPU. If they make a build in eGPU 5K display, I am quite sure the cooling system will just barely can cool down the GPU. Any real stress to the GPU will cause overheat straight away. That can explain why the Apple may not allow us to utilise the eGPU inside the display, and that sounds like more the Apple way of doing things.
