Some people did used it for homebrew, search for waluigi simulator or Super Mario Kart 3D. You obviously can't use 3DSX files tho, so you need to be able to install CIAs.
The 3DNES emulator runs pretty slow on my pc, and it was a pretty good pc... about 4 years ago (although the 1.3.0 update did speed things up a bit). so I would assume it would run like crap on the 3ds. I'm not sure about the new 3ds though.
