I'm using mopidy now for about a year and i'm quite happy with it. I've setup a multiroom audio system based on mopidy in my home and wan't to share idea. Maybe it could be included in Mopidy somehow. Basically this solution consist of one master device and couple of slave devices. The master device act as an audio source and slaves acts as audio recievers. All devices runs Mopidy, plus master device runs rtspserver service based on this code (Mopidy sends audio to this rtsp server, and rtsp server sends audio to all connected clients). All clients can use Mopidy normally or choose to play rtsp source stream to play the same audio in sync. So if You put a client in every room you can have different music played in every room or the same music in choosed/every rooms. The master device can also play audio in sync if it will use the same rtsp source (of course not with Mopidy instance that serves the audio for rtsp server, but maybe with another Mopidy instance or just a simple gst-launch command). Of course there is more to explain, but I think that thats enough to get the idea. Oh, and with rtsp and gstreamer You can send lossless or compressed audio, depending on your connection bandwidht, wifi can be tricky, i'm using compression and 5GHz band wifi (802.11ac) and it works 99.9% of the time without any glitches and sync issues. Using etherenet cable propably 100%.
As for the integration of this into Mopidy I'm thinking about some kind of 'Share' button that will start the rtsp server and clients that could display avaliable rtsp sources (using avahi ?).
Tell me what You think about this ?