Note that this is what CAMM[1] memory is intended to solve, although it remains to be seen to what extent it catches on.
The problem is that these are integrated shared-memory systems with a single RAM pool. That's nice for a lot of reasons, but GPUs need many more memory channels and larger bus widths than CPUs do in order to do work and remain fed at a reasonable power draw. It's an inherent design trade off. I don't see a CAMM style solution for GPU memory coming anytime soon except on the low end.