Would it be possible to make a homebrew app that would run on the DS (or 3ds in ds mode) which could contain a collection of 3ds files. The app might be something like moonshell or linux based. You would boot using the gateway blue card, then put the microsd card from the red card into the SD slot. Then you would simply select the desired rom, and the app would then format/write it to the sd card. This would make it possible to switch ROMs on the microsd, on the fly without needing additional hardware.