Yes, there's two on the market right now (Power Pak and the Everdrive) but I was thinking of making my own to address the shortcomings of both, and to make it do just that little bit more.
So the bullet points would be:
- * Full mapper support - including MMC5, mapper 90, etc
* Full expansion audio support like the HDMI adapter
* 1/8" stereo jack on the end of the cartridge that allows you access to line out stereo audio - no system mod required
* Audio would also exit in mono form on the usual pin for those that want an audio mod
* Digital audio is possible, since it will use a DAC so spdif and similar would be a theoretical option
* Gameboy support - ability to play GB ROMs natively on the cart with the NES outputting audio/video for the game
* SD card running in 4 bit mode for instant game loads
* Save states on select mappers (i.e. MMC1, MMC3, etc)
* Game Genie support of course
* USB to download code to test instantly
* High resolution menus using a 5 pixel high variable width font
* Low resolution menus using a 7 pixel high variable width font
* NSF playing with visualizer
* GB link port - you would have to transplant an existing GB link connector though
* CopyNES lite
I figured since the existing flash carts on the market don't really do everything I want them to do and the odds of them being able to do so is slim to none, a new flash cart might be in order.
I have all the mappers done already on the FPGA NES so the mapper thing isn't a problem, and the FPGA gameboy is done also, so getting it to play GB games is not a problem either. For the variable width fonts and 5 pixel high text mode, I was going to have a CPU on the FPGA handle most of the menu stuff, with the NES merely acting as the output device. This frees me from all the vagaries of the NES graphics restrictions like waiting for vblank, and even the notion of tiles is completely made irrelevant. I can easily produce a full bit mapped NES display on the FPGA with it handling all the dirty pixel -> character translation, and I can even do 8 attribute changes per character.
So, what do people think about this type of thing? I am not sure if there is a market with the existing carts out there, but the complete(ish) mapper support and gameboy playing might push it over the edge. Cost would be in the $120-150 range probably.