I could see the 3DS being able to handle an N64 emulator. It has plenty of fast memory and a solid GPU that can render tons of polygons. The CPU is still rather unknown besides being ARM11-based, the clock speed and number of cores is unknown (some sources were claiming it was a dual core ARM11 clocked at around 266mhz). I'd hazard a guess that at least a few N64 game could be gotten to work with the system (if not the more powerful games). I could easily see N64 games working better than the PSP emulator can do, seeing as the 3DS is a lot more powerful.
Of course, this all assuming the system EVER gets hacked for the general public and homebrew developer manage to make games for it.
Remaking or porting N64 games is not the same as emulation. You could easily remake an N64 game and make it look miles better than the original, but if you emulated them they'd look no different and wouldn't play nearly as well as they would if you specifically coded the game for the system.