The DS has only 4 Mb of memory.
It takes 4 (or 8) Mb to emulate the N64 RAM + the memory footprint of the emulator... See the point?
Furthermore, there is no binary compatibility at all between the R4xxx family and the ARM family. To get half decent speed on such a processor (ARM9 at 67 MHz + ARM7 at 33MHz, remember a 200 MHz P II was a bare minimum to run Corn), you'd need a very hackish dynarec, and efficient dynarec eats a lot of RAM for it's complied code cache.
