But whether or not it could actually be done or done well is yet to be determined. Nintendo handhelds aren't fit for emulation though. The best devices to emulate Nintendo games are non-Nintendo devices.
There must be atleast a dozen tablets in the $130-$150 range that can emulate PS1 and N64 better than 3DS could hope for itself.
As long as you have enough stones you can emulate a PS3 in stones. Same thing goes for emulators on the 3DS. Whether they're fast enough to be considered playable is another matter entirely (and unknown).
The problem with emulators is that you're essentially translating machine code from one CPU architecture to another, in this case MIPS to ARM (N64/PSX to 3DS), and that's not going to be easy in the least. Snes shouldn't be an issue, nor should Genesis and GBA, maybe, since the Ambassador program has GBA games running at full speed, but then again, the GBA used an ARM7TMDI CPU. But N64? I wouldn't get your hopes up.
Tbh, i dont think its possible for the 3DS to be able to run such emulators. In DS mode, the CPU is limited and in 3DS mode, it is consantly checking everything such as battery level, screen brightness, friends online, nearby players and such.