I guess they can:
So basically this card + a DS2.
- Put a physical switch on the cart to switch from DS to 3DS mode.
- To switch 3DS games, boot in DS mode, run app to switch games on the card, boot to 3DS mode. This is somewhat similar to how I swap games into my slot2 cart.
I gave some more thought to this and perhaps it would be possible for the card to automatically decide to boot into 3DS or DS mode and not need someone to play around with a physical switch:
- By default, the card boots in DS mode and straight into the rom selection menu.
- Choose a rom and the console is rebooted. The card will automatically switch to 3DS mode upon a reboot and run the selected rom.
- To get back to the selection menu, you have to turn off the console and turn it back on.