Create a bluetooth receiver that can be plugged into a stereo/speaker which can be paired multiple bluetooth devices. Not playing simultaneously (not possible without a mixer), but can maintain 2 or more bluetooth connected devices and auto-switch to the active input based on most recent new audio signal received automatically.
Benefits are that you can turn any existing stereo/speaker into a bluetooth connected device that can be connected to multiple devices (e.g.: several smartphones in a household), without the need to constantly un-pair/pair different devices, or select which input to use manually.
May require several bluetooth radios, and a smart switching circuit? Ideally a switch action would also pass a pause/stop command back over bluetooth to the previously active playing source.
A challenge!
