[tarlinian]

Mainly because what you're saying isn't true for many workloads? (Also this already works for most existing integrated GPUs.)

The types of workloads run on GPUs typically like very high memory bandwidth and are usually willing to live with higher memory latency to get it. Onboard GPU memory is usually built with this in mind (trade off capacity and latency for increases in bandwidth). This is generally speaking the opposite of what you want in a CPU where people often want very high memory capacity and lower latencies, but may not limited by memory bandwidth, so simply sticking a GPU on die and giving it access to a memory subsystem that was not designed to feed a GPU is not going to make anything better.