Recently there have been a few posts on the main forums along the lines of "why can't I use MC to push this or that radio stream / video stream etc. to my DMR".
And they have a valid point. It would be cool if MC could do this.
And more to the point, it would I think be trivially easy for MC to add that feature. Today when MC pushes a local track, it sends a SetAVTransportUri command with the URL of the track on MC's server, then it sends a Play command, and then the renderer downloads the track from MC's server. Now in the above process there is actually nothing to prevent the SetAVTransportUri command passing the URL of any track on any server anywhere in the world. And then when MC sends the Play command, the renderer should go off and download that track from wherever it is located. Basically MC just hands off the remote URL to the renderer and lets the renderer get on with doing its own thing...
You would need some logic to stop MC trying to push a Next track when playing in this mode. But otherwise I think it is trivial.
Of course there will be cases where the renderer can't get through the firewall to download the track. And there will be some cases where the renderer cannot play the media format. So in those cases you could eventually consider making MC into a proxy server that pulls the remote track and re-serves it on to the renderer. However I think you could get a lot of mileage from the above mentioned simple remote URL hand off process before you need to start losing sleep over making MC into a proxy server.