Hi. not sure if there a product already in market. they seem to be all flash type.
the gold is to give a new life to my old laptop that has only 255MB ram and 512kb max upgradable. its a bit slow linux and virtualbox apliances and hard disk swap partition.
there are people using usb flash devices as swap but they all warn about fast damaging usb devices.
so way not an adapter ddr3 to boost memory on the fly to old computers like laptops, raspberrypi, old 486 computers or maybe even tablets.
maybe also implementing a software that would manage withch programs run on original memory and witch run on usb ddr3 memmory device