I have a programmer friend of mine, We've been talking for awhile about making games together. He Programs I design, we find an artist. The idea of making an 8-bit game came up, then I found out about the Winner is You cart that Retro USB has that has actual recorded music on it and comes on a 64MB cart. So that got us thinking about how far beyond the limits of the NES could you go in theory?
The problem with sample playback on the NES is for the really high quality stuff you are going to essentially use all the CPU time. You could use the audio input on the cartridge connector (Famicom, Expansion Connector for NES) and feed in whatever mono audio you want. As for video you're going to be limited to the 64 sprites with 8 per scanline no matter what. However you can feed in whatever you want for the Background. So you could have a bitmap with the limitation that every line/segment of 8 pixels has to share the same 4 color palette. And of course you could have whatever processor you want to do all the actual processing for whatever you are doing, using the NES only for its audio/video and input but not actually for game computations. Not really much of a NES game at that point. Was there something specific you were wondering about?
I'll have to have my buddy join in, we're still kicking ideas around for exactly what we'll do. It sounds like if we were going to do a game with I guess Live audio we'd need some sort of special cart that might not exist. If we use a large cart it might just be to increase the scope of the game. Then there's the matter of game saves, would we be bound by a battery or could we use flash memory, and again does such a cart exist? What we're cooking up is at least in theory, something emulators would struggle with but not actual hardware (which would include the FPGA systems)
Yes, you could use Flash Memory or some other non-volatile memory for saving data. There are some homebrew cartridges with that capability. Whatever you are hoping to do is probably going to require creating your own cartridge hardware, which unfortunately means without modifying an emulator will leave you without the wonderful debugging capability of modern emulators.
