The DSL and DS are both incompatible with GBC/GB games.
As in they don't even fit in the slot.
This was the worst thing about the DS for me.
It's the reason I loved the GameBoy Advance/SP, because it could play GBA games and GameBoy/Color games.
Then the DS cuts out a large chunk of the games existing for the Gameboys.
And then 3DS got even more stupid and they removed the GBA slot, so you can't play any of those on it.
And special games, like Guitar Hero GBA used to have a Guitar Hero key-pad that would plug into the GBA slot to play with. Those are completely impossible to play on a 3DS now.
These looks really really cool. Would love to do that, but I'm not sure any of my GBA's are in good enough condition, and I'm not sure where my SP is.
Good luck with the project though. Looking forward to seeing any progress with it.