http://www2s.biglobe.ne.jp/~tns/nr641101.html
neat.
Quote:
"At Comic Market 67 scheduled on Dec.30th, WeirdDeviceCorp will start selling a cartridge that allows you to play NSF music files on the real FAMICOM hardware. It uses SD memory cards (up to 64MB) for file transfer, and also features 3.5mm audio mini plug, and will be open price. Note that only NSF files using mapper 0 (up to 32KB) are only supported on the cartridge."
neat.
Too bad they don't have a cheaper model that simply reads and plays mapper 0 NES ROMs from SD cards 
Would make developing quite a lot easier...