You can get ECC DDR3 ram for less than $1 per GB, and it doesn't wear out like SSDs do. Makes a lot of sense for a cheap cache disk. I can totally see using a ram disc like that for a zfs/bcachefs cache with a modern CPU that doesn't accept DDR3. Might make more sense to use PCI than SATA though.

A niche market, but I think there would be a market for ram drives like that, especially if they supported ECC memory. Lots of old server memory kicking around but if you want to actually use it your stuck with some abysmal CPU performance and a very high CPU power draw.