Psst, all it takes is a dot of solder to connect the 2 pins on the side of slot-1I own a DSi, and this game selector to switch between any of the 3 inserted Slot-1 cards without powering down the card slot.
He's the well known Olimar/Loopy, and even back then he said it was hard enough to get it to this level so he wouldn't do it again for the DS Lite firmware so...Has anyone ever contacted the creator of the firmware.nds file about adding back Slot-1 reading?
How would you practically use it anyway? For now, a DSi-compatible flashcard is the only way to run a .nds with slot-1 access on a real DSi...!