Alright guys, two links:
http://www.neoflash.com/forum/ Down at the moment, but they are working on an SNES, genesis, and N64 flash cart which is supposed to use USB and have the option to use a flash card through a game boy advance flash cart (strange idea i know). They released a crappy version of the sega genesis flash cart which uses parallel and only has 32mb. However, these have been in the works already for at least a year with no end in sight. Dr. Neo has a ton of projects and unfortunately the market for the gba and ds flash carts seem to push the vintage devices to the back of the line. I do believe that eventually they will come, but in the mean time I'm going to purchase the tototek versions.
http://www.nespowerpak.com Here it is, the one we've all been waiting for; at the risk of flooding the demand for these, the nes flash cart. Uses a compact flash, the mappers are on the flash card so they are easily upgradeable, and the bios itself is upgradeable through the vendor. I know it looks like a joke, and I can't say with 100% certainty that it isn't a joke, but it's been in development for quite some time. The threads are over at the nes dev forums. Best part is, it's actually coming soon, 100 boards have been made, he's just waiting on the cases. Most of the major mappers have been finished besides MMC5, so he claims it will work with all but like 10 games.
Sorry that the one link doesn't work, and the other is only preliminary, but everything I've stated so far is as accurate as I remember it.
--PS