I fully agree about the SID still being relevant: If you look for example at the Adlib, it has lots of voices, the frequency modulation can generate very interresting waveforms, but it lack the capability to do smooth transitions.
The SID can do:
- Smooth transitions in pulse width
- Smooth transitions from one note to another
- Smooth transitions in the filter
The Adlib can do none of these, even the frequency control has too low resolution.
And yes I agree the sound has become a bit stale, so it makes a lot of sense to add more waveform possibilities. My message is just, that besides the four basic waveforms, the SID has the filter and ring modulation to synthesize more complex waveforms. If you want to enhance its waveform capabilities, you should look both to the basic waveforms, as well as into possibilities to empower composers to do more with ring modulation and filtering, all three of them are waveform tools.