> ...Don't SD card loaders already exist for the DC?
While indeed they do exist (2009?! how is it I didn't know about it until now?), from what I've researched so far the serial port has limited capabilities and you can't play the games without hiccups.
So, unlike an ODDE it's not a 100% reliable option. I may try it in the meantime. Now I need to desolder an AGP port in order to build a serial connector instead of modding the console.