"Respond over Media Source" is highly welcome! I hate how the car goes into phone call mode whenever I ask Siri for anything.
Would be nice to also have "Always respond on iPhone speaker", keeping bluetooth devices away from Siri entirely. I don't need the whole party to hear Siri's response if I ask it something when playing music over Bluetooth at a gathering, etc.
There was also the option several years ago to tell Siri which microphone to listen from. Back when it was full screen only, there was a little Bluetooth icon in the bottom right. That went away when the full screen interface did and was never replaced.
So in my car if connected via Bluetooth it only wants to listen to microphone input via the ****** car microphone, not its excellent built in microphone array. And there is no way to tell it not to.