Have you thought about supporting the creation of RAM disks in a GPU's video RAM?
With today's VRAM sizes, as well as the fact that the 32 GB barrier is approaching fast (by that I mean the necessity for having more than 32 GB, i.e., 64 GB typically in a system), this is becoming an increasingly viable option.
As far as I know, there is only one no-longer-developed tool for VRAM disks, GpuRamDrive on github. While it works, it's an experimental solution which appears to be much slower than traditional RAM disks (~2 GB/s vs. ~10 GB/s on my system).
The rationale for not using GPU is basically what you have just mentioned:
It's much slower than RAM and may even be slower than SSDs.
It's expensive as GPUs with a lot of VRAM doubled and tripled in price recently.
I am not familiar with the "32 GB barrier", e.g. we have a system here with 96 GB of RAM and it's 5 years old. Most modern motherboards should support over 32 GB RAM, except some laptops. So in a typical desktop PC you could have 128 GB of RAM costing less than 1 GPU and use a regular RAM disk as needed.