I have an idea for a 3DS flashcard based on Crown 3DS, GBA Exploder and EZ Flash 3-In-1. Similar to if you were using a DS Lite with a normal DS mode Slot 1 flashcard and an EZ Flash 3-In-1 in Slot 2 where you would have been able to choose ROMs through the Slot 1 running GBA Exploder and when you selected a GBA ROM in NOR mode it would have written the GBA ROM to the EZ Flash where it would make a 1:1 copy of a GBA Card and you could run it though the normal DS firmware. The card will have a switch on top of it, when the switch is on one way it will use the first memory chip and when the switch is flicked it will use the second memory chip. On the first memory chip is a regular DS mode flashcard however, when you are in this mode if you select a 3DS ROM it will write it to the second memory chip inside the flashcard. When you flick the switch to use the other memory chip which has the 3DS ROM on it, it will act like a 1:1 copy of a 3DS card, just like Crown 3DS would do however you can change the ROM directly on the 3DS without a computer by switching back into the DS mode part of the flashcard. Do you think this could work? It would be quite expensive and might even need to stick out a bit like the early Action Replays but it might work.