n64 emulation is very unlikely. the DS itself is comparable in power to the N64. it would be like having a ps2 emulator for xbox.
the golden rule of emulation is the 10x rule. this means that the machine emulated has to be 10 times weaker than the machine that is emulating it.
psp emulation of n64 is currently very slow, about 15 fps for games like mario 64. it may yet reach 60fps, but games like goldeneye or conker's are out of the question even for psp.
honestly, i'd be happy just to see really fleshed-out emulation for nes, snes, gbc, genesis, TG16, and other weaker systems. the scene for psp has these emus down pat, and the DS can certainly handle them.