Using a Cyber Gadget CodeFreak game capture utility, one YouTube user has found the 3DS will run backed-up games and even homebrew applications. As crazy as that seems an R4 cart also seems to work on the 3DS. Another YouTube user has discovered that right now the 3DS will played backed-up games from an R4, since it recognizes it as a DS cartridge. Of course, Nintendo could kill compatibility at any time through a system update.
Is this surprising to anyone?