> since Dolphin already does that it may be just as simple as adapting
> the SIMD instructions into Altivec instructions.

It's the "simple" part I'm doubting. And I don't think it was "simple" to map Gekko's/Broadway's SIMD to SSE in Dolphin. But then, I'm not a coder and even less a SIMD expert, so there might indeed be people who'd do that as a warm-up exercise ;-)

> of course, it would eliminate the possibility of G3 Peg and
> eFika users from using the program, since both lack Altivec.

Yes, that's why earlier in this thread I mentioned the possibility of translating the SIMD code into scalar code with the drawback of even slower execution on slower CPUs such as G3. On the other hand, Gekko is a G3 running at 486 MHz, so the Efika 5200B with its 400 MHz G2 surely wouldn't be able to emulate/virtualize a Gamecube at full speed anyway (that's even before taking the heavy RAM constraints into account). And given the required SIMD to scalar code translation I guess the Peg's 600 MHz G3 could also have problems to do this.
In conclusion, I think that anything below G4 wouldn't present a viable target hardware for such a project.