Such a 12v trigger would be useful for a plain stereo amplifier, which are relatively simple things -- so simple that they may not even have a volume control.

Such a 12v trigger would be useful for a plain stereo amplifier, which are relatively simple things -- so simple that they may not even have a volume control. This would allow a Sonos Port to have a dedicated amplifier connected (for driving one big stereo pair of speakers, or maybe an array of 70v distributed audio speakers, or who knows what) and control when it is powered on. But it won't turn on my AV receiver (it has 12v triggers, but they're all outputs), nor switch its input mode appropriately. (Yeah, sure. I can hack something up with an ESP32 with IR or RS-232 or even Lego Mindstorms or something from Switchbot, but Sonos buyers and hardware hackers are naturally somewhat diametrically opposed: A person who buys Sonos gear wants stuff that just works, not a new hobby.)