The SA-1 (the chip used in Mario RPG) was basically a supercharged SNES on a chip. Additional RAM and processor clocked at 12mhz (the original SNES processor clocks at about 3.78mhz). When initial emulation of the chip hit for PCs it pretty much doubled the system requirements. But I'm not sure if this was merely because of emulating the more powerful chip (alone anyways) or if a large part had to do with the fact that it added yet another timing issue to deal with.
If you don't have all of the chips timed correctly, you get a lot of bad things happening, including game crashes. This was a big problem emulators had when they first started adding sound (both for PC, and even more so on DS since each chip was emulated on different physical processors with different timings) Adding an additional processor you have to emulate and get the correct timings to to keep all 3 in sync (CPU, SPC, and SA-1) would be a real nightmare and not something I think you could even manage with the improved processor of the DSi.
