For windows I saw something similar to this years ago. An experimental proof of concept driver that allows the creation of a ram drive from vram for NVIDIA cards. Sequential is fast as you'd expect, random has lots of room for improvement.
>GpuRamDrive
>Create a virtual drive backed by GPU RAM.
https://github.com/prsyahmi/GpuRamDrive
Fork with AMD support:
Thanks for sharing this, good read :-)