I am thinking it is because AMD is ready for directx12 which almost the same thing of apple side "Metal". recently i have tested the ashes of the singularity which is the first fundamentally directx12 supported game with my m395x. i figure out my card gain around 15% improvement on directx12 which almost 80% more frame rate compare with GTX 970M and 10% below 980m. Would likely to see more performance gains on directx12 by driver update later. Therefore i don't think apple will shift to nvidia on the coming update.