I dont see how this helps Apple to compete with AMD or Nvidia GPUe. It's much easier for Apple to just use AMD GPUs for their Pro devices. Macs market is just too small to create custom high-end GPUs.
Apple might have huge leverage on mobile with iPhone because Android graphics drivers are horrible mess, but on Windows GPU drivers are decent and building custom driver stack sounds like too much.
I guess because one can't just reuse hardware. They cant just take iPhone GPU, make it 5 times bigger and get 5X more performance with 5X of power budget. So more likely they'll just gonna sell laptops with GPU performance closer to iPhone which is not at all impressive.
GPU is actually relatively easier to scale by adding more cores/ALUs. The difficulty lies in figuring out how to handle peak current requirement of the whole IP.
Apple might have huge leverage on mobile with iPhone because Android graphics drivers are horrible mess, but on Windows GPU drivers are decent and building custom driver stack sounds like too much.