We already support Raspbmc in fact - the only thing on your list we don't have is an XBMC plugin to control Dianemo or the control from an Orbiter. But everything else is there. After all once you add Raspbmc to Rpi you have one of the best full featured & open media players you can buy.
Sounds good. Maybe the QOrbiter or HTML orbiter can be add as a plugin. You mean that you cannot control XMBC from another orbiter? That seems like important to be able to use TV or did you solve that differently?
What is then still missing if those 2 points are added? Maybe rs-232 and usb uirt control support? I suppose squeezeslite is already supported?