Let's me start by saying that I am indeed not too enthousiastic about just adding voices. There are quite a few "many SID" tunes on Youtube and if you listen to them, you hear that the composer just waste them by using them for chords. They do non e of the things that makes SID music sound great. Now the inability to do chords was surely something that drove SID composers crazy, but also something that motovated them to find alternatives and it is those great arpeggio's that make what the SID is known for. Therefore, just trhowing more channels at composers is not going to get us better music.
- In many games, 1 channels has to be reserved for sound effects
- If you use ring modulation (one way to create non-standard waveforms), you loose one voice.
... and especially those such situations I consider 2 voices really too low. Yes, the Mega65 has samples, which will help a lot, but nevertheless, I think the number of voices does need a close look, but it is something that should be done with care, and more=better is probably not true.
I think you super and natural waveforms sound great!
For the natural saw though, you can get quite close to it already by filtering a normal sawtooth. You don't get there completely, as you cannot make the "drop" 100% vertical with filtering, but it will look similar. Question is of course how close they would sound, if there is a difference, there would still be added value. That 100% vertical drop will have a an effect on upper frequencies, so may well have a rather large effect on the tone.