We actually had real-time save cartridges way back in the C64 days... google ISEPIC, Final Cartridge, etc. Their purpose wasn't to allow real-time game saving, more like a cracking tool, but some of us used them to save states in games that didn't allow saving (or didn't allow multiple saves).

The DS is a much trickier beast than the C64, but ISEPIC appeared only 2 years into the C64's life and it's been almost a decade since the DS came out. I could believe someone found a way to get the program counter and registers of both CPUs, and dumping the RAM isn't a big deal. I don't know what other state information needs to be saved... certainly things like network connectivity won't be.

Neat to still see new unauthorized DS hardware being produced. Now, if they can do even a homebrew-only flash cart for the 3DS, I might actually be tempted to buy a 3DS. Till then, I have three Android devices that'll play games, soon to be four. Not the same as the 3DS, but I'm done buying hardware I can't hack.