Using two GPUs for rendering (or rendering + compute) is a lot easier to do with DX12 and Vulkan - there are some benchmarks/game engines out there that can do AFR across paired GeForce and Radeon cards, for example, and it actually performs really well. So with Vulkan you could probably utilize both an Intel onboard GPU and a discrete GPU simultaneously. The question is how much leverage you can get out of that, but I bet people could come up with good uses (rasterizing font glyphs or doing some computational work, perhaps)