Earlier quoted context omitted.
I wish people had continued this sort of thing, I had a Gigabyte i-Ram[0] and it was incredible. The most limiting factor was that it used DDR memory slots (maximum 4GB) and the SATA interface. I don't imagine there would be much of a barrier in doing this with more modern technology like PCI-e for the transfers and a big juicy FPGA for addressing substantially more memory. Alas.
Problem is the maximum capacity due to memory controller support more than anything else. But looking at the new NVMe SSD's the bottle neck isn't your SSD anymore and they aren't that expensive if you need those speeds for things like 4K video editing...
Yeah, I like the concept more than have a need for the thing presently. The OPs page talks about a custom spun ASIC so making a controller wouldn't be a huge problem if someone wanted to sink the NRE into it.