Not really. See below.
Well, I've been tinkering with the latest version of FCEUX (NES emulator) last few weeks.
But I don't want to get anyone's hopes up. My progress's been really really slow, doing small little things at a day. I've got the bottom screen UI ported over from SNES9x for old 3DS, minus all the cheats, savestates, sounds, keypad inputs. The previous effort refactoring the SNES9x emulator helped a little. Now it can actually boot games (no sound yet) but rather slowly at 45+ fps on an old 3DS (simple mappers).
Rendering is still totally software-based. The rendering loop is simply spending too much time copying and transforming the NES 8-bit paletted framebuffer to the 32-bit 3DS RGB framebuffer (almost 30% of the time!). Spending a bit of time trying to optimize this.
From what I've learnt reading codes thus far, the complex mappers can be fairly computationally intensive. But that remains to be seen... I haven't tried booting into those at all.