DIMM slots won't work for GPU VRAM due to the higher speeds, tighter signalling, and dense packing of memory on wide buses. Take a look at the speeds DDR5 is running at in a typical Xeon server, and compare to GDDR6. This is the problem LPCAMM2 was developed to solve for modern x86 CPUs in laptops and desktops. Seeing it applied to GPUs would be great.