I don't know why this idea got scrapped, it seems like it would be perfect for today's amps. It was more common on radio and military equipment. I think I might have seen one guitar amp on the net that had one octal cap, but it doesn't seem like it really caught on with guitar amps, They were generally dual (2 caps in one can). Relays with octal or other bases were also common. In amps I've also seen octal connectors with a cable for connecting the switches and pots to the chassis, or several chassis together.