Flashcarts do work on the NA 3DS. I was at a demo event at my nearby shopping center to see a huge crowd frolicking in the middle. Turns out they're playing with 3DS consoles.
I had my dad keep the Nintendo girl's back turned while I sneakily stuffed my SCDS2 into the thing. It runs. Nuff said.
I cut it really close though!
Source- myself.
Source- myself.