They certainly have made a custom flashcart, like they did when they dumped their fully working DSi roms.
As long as you can send to the 3DS what it wants to hear, it will work, guaranteed.
3DS Mode flashcart is possible, but maybe not like we had known them, with their menu/soft reset/cheat codes, Nintendo has strengthened their security (the DSi now refuse custom icons/text), the 3DS certainly checks what's run in 3DS mode, and gives a "An error occured" if it's not on the whitelist (I mean when the flashcart switch from the faked game data to the homebrew menu binary of the flashcart).
only possibility left are the good old single game flashcarts , the 3DS wants to read 01001001, you give it 01001001 at the correct speed, it will work (and then people will whine about their skinned menu/soft reset, but that's another story
).
As long as you can send to the 3DS what it wants to hear, it will work, guaranteed.
3DS Mode flashcart is possible, but maybe not like we had known them, with their menu/soft reset/cheat codes, Nintendo has strengthened their security (the DSi now refuse custom icons/text), the 3DS certainly checks what's run in 3DS mode, and gives a "An error occured" if it's not on the whitelist (I mean when the flashcart switch from the faked game data to the homebrew menu binary of the flashcart).
only possibility left are the good old single game flashcarts , the 3DS wants to read 01001001, you give it 01001001 at the correct speed, it will work (and then people will whine about their skinned menu/soft reset, but that's another story