Had a RAM disk circa 2005 was a fun experiment especially when you could fill it with very cheap DDR 266/333 modules but it wasn't really useful.

You could maybe get 8GB in those days usually you would get only 4GB while it was possible to put an entire game or at least the big chunks of it on there or alternatively some video content it was clear that it would never get anywhere.

They are still much faster than SSD's the problem is not even the cost but it's the fact that none of those can any meaningful capacity even beyond the physical limitations the memory controllers we have just can't support a capacity which will be worth while..