redNAND
It seems to be doing the rounds well enough but Smea/Smealum is back with another nice little demo. It builds off his previous work so no release as yet but what it does is redirects the 3ds' read and write requests for the NAND (which holds firmware and the like) to the SD card instead, albeit a partitionless space after the main partition. This allowed Smea to launch the current 6.3 firmware and do things like eshop and games that need post 4.5 firmwares all while keeping on a hackable firmware.
Discussion is continuing on the original custom firmware thread and of course IRC
One twitter post for those that like that sort of thing.