Is the GPU going to be MXM 3.0 A? I'd say that would make sense for a 15 inch laptop. From what I saw, AMD's R9 M270X would do rather well, and at a fairly nice price. However, it has a TDP of 50W, and I could imagine a lower TDP being nice for a laptop without low power integrated GPU. That or we could try to add a PowerVR or similar low power GPU for basic rendering and work on hardware or (kernel level) software switch, along with drivers if needed.