Any seperation of a GPU from its VRAM is going to come at the expense of (a lot of) bandwidth. VRAM is only as fast as it is because the memory chips are as close as possible to the GPU, either on seperate packages immediately next to the GPU package or integrated onto the same package as the GPU itself in the fanciest stuff.

If you don't care about bandwidth you can already have a GPU access terabytes of memory across the PCIe bus, but it's too slow to be useful for basically anything. Best case you're getting 64GB/sec over PCIe 5.0 x16, when VRAM is reaching 3.3TB/sec on the highest end hardware and even mid-range consumer cards are doing >500GB/sec.

Things are headed the other way if anything, Apple and Intel are integrating RAM onto the CPU package for better performance than is possible with socketed RAM.