I'm doing 16bit math on the machine all the time for what I'm doing right now. Its not that difficult.
_And_ Mahoney did 8bit samples at 44100Hz on the C64. Take a look: http://csdb.dk/release/?id=129090
I was sure the Amiga did 12bit samples. Never mind.
I just think that if we're going to add waveforms to the SID, a sine is an obvious (but probably last, like you say) addition.
Sorry I made a mistake. I was thinking "natural" saw instead of reverse which is somewhere between sine and saw and sounds more like a real instrument.
"Super" saw is basically the same as three saws at the same time: usually something like the base note + one at -5 semitones and one at +7 semitones.
Having these would free you to do other things with the filter and other voices.
Having a real white noise would probably be nicer for percussion than the current noise which I find to be quite pink.
Most synths these days have these types and it would be nice to "step up" the SID.
It doesn't matter really. I think changing the SID would be very difficult anyhow.