So, I think the thing everyone seems to forget about graphics hardware is that a HUGE part of performance and features is based on the software stack they have running over the top of them. And these software stacks are extremely complex, including things like sophisticated memory management and JIT compilers for shaders.
NVidia and AMD have been evolving their software for probably over a decade now. They support multiple versions of both DirectX and OpenGL, all on the same basic hardware.
Intel on the other hand, doesn't have any of that software (that I'm aware of). They are essentially open sourcing their hardware and pushing the development of the open source software stack (Mesa, Gallium/LLVM, etc) as the preferred software solution for their hardware (at least on Linux).
So, while I expect Intel could build a piece of hardware that performs better at a hardware level than AMD/Nvidia could, by dint of their process superiority, the software side of things is still several (3-5?) years behind. As a result, they'd probably still lag behind significantly in performance. And all the spiffy hardware in the world won't fix that.