I'm sorry this is not a specific addon support question, more a request for information about addons.
I've a long term plan to rule the devices in my house :). Part of that includes using one set of bluetooth headphones to simultaneously receive audio from multiple devices, such as libreelec and my laptop or another PC. I really don't know much about gstreamer, but a friend mentioned that it might be able to help to act as a network mixer for bluetooth output.
Otherwise I'd like to ask about addons and advice that can help me achieve this. I didn't see gstreamer in the list of addons, and am not aware if other tools or libraries are capable of sending ALSA audio elsewhere.
While I like to avoid duplicating efforts, I will build my own gstreamer addon if needed.