Way back when, Gigabyte came out with a cool product, the i-RAM. Was a pci card that took 4x ddr dimms to provide a 4G ramdisk, sata1 (yes, old 150) interface, and it only used the pci slot for power.
Works great, if not the speediest demon. It's limited to 4G though, and the slower sata1 interface.
Then Acard came out with a cool device, the ANS-9010. That is a 5-1/4" bay box with 8x ddr2 dimm slots and 2x sata2 interface port. Better, costs about $400 or so I think. The 2x sata2 ports let you split the ramdisk in two and raid0 them for additional throughput. But ddr2 is expensive, and you're still limited to the sata2 interface, which is abysmally slow for a ramdisk.
FusionIO is the golden standard, using pciE cards with nand flash on them. Up to 2TB or so. With a gold-plated price to match. We're buying two of the gen1 640G cards at about $14k EACH. Dayummm.
I think there would be a great market for a pciE card that held at least 8x ddr3 dimms, which are almost cheaper than dirt now. Use a typical molex connector for additional power if needed and at least 8 pciE lanes for throughput. Add a usb3.0 port for a flash drive to back stuff up to non-volatile, and a battery to actually do the backup if power is lost.
Keep that to around $400 or less, and I think those would sell like hotcakes. So, would need a ddr3 controller and a pciE interface, and some glue logic and code. A fairly simple device driver, similar to the FusionIO one, to present the ramdisk as a block device.
So, anyone out there wanna make this ?