Ah, I see... I didn't know it would require a significant amount of CPU time to read that way. It just got me wondering because you said the DPC+ wavetables are stored as 8-bit, but the TIA's volume register is only 4-bit, which means the 8-bit amplitude values of the DPC+ wavetables would need to get rounded to the nearest 4-bit integer at some point anyway. It seemed like it was worth a shot for 2x the storage efficiency. Perhaps that kind of bitplane compression would still be viable for saving space in ROM, if not in RAM? I dunno, maybe...
Yea, that'd be optimal for having different musics in the game that have different wavetables! You'd only load up the wavetables you need into RAM while that particular song is playing.
Most chiptune tracks I've made with wavetables on the PC-Engine and N163 thus far rarely if ever use more than 16 or so unique wavetables. I'd imagine with the 2600, as long as you had your basic waveforms (various pulse widths of square, a sawtooth, sine, triangle, and maybe a slap-bass wave) you'd be all set.