Couldn't someone theoretically just make a patch that makes the TWL_FIRM save all saves to SD card instead of to the DS cartridge?Emulating DS on the 3DS? No. Virtualizing it using existing hardware? Maybe.
Much like proper DS mode on 3DS, you'll have to code your "DS Emulator" to use execute DS code directly on Arm11. But this could be difficult to impossible to do correctly. NDS was mostly Arm7 and Arm9 which is why the the 3DS has to reboot into DS mode to play DS titles since Arm7 is not accessible in CTR mode.
So you'd have to find a way of getting Arm7 code to run on Arm11/GPU which I believe is what CTR games uses. Good luck with that as it would not be simple at all. Since DS mode flashcarts are still a thing on the 3DS there is little incentive to really bother with this. You could try and patch TWL_FIRM's RSA checks so you can build custom DSiWare and convert DS games to DSiWare and run them that way.
But DS games are meant to access Slot-1 and save on Slot-1, so you'd have to either patch each and every single game you want to use or find some way of creating a DSiWare app that does it. But some of the prominent devs here have said that doing that isn't possible, so I hear you have to instead try and patch the game instead. It doesn't seem to be worth the effort at the moment unfortunately.
Yikes. I didn't know. (Unless you're referring to someone else. )How many times have we seen this question? taking a wild guess, at least 15 by now
Asking anyoneYikes. I didn't know. (Unless you're referring to someone else. )
definitely possible. hard to gauge how good performance would be, and it would take a ton of work, but there's no real reason why it couldn't be done. at the end of the day it's more a question of whether anyone would want to work on it considering the limited benefits such a solution would have over just, you know, using the built-in backwards compatibility stuff.