For non-Dianemo users, I think I am right in saying that no option exists for controlling a lightweight non-MD no-orbiter generic media device?
I think phenigma's work on the RPi MD looks exciting and I'm looking forward to trying it, but if there were an option to install some generic media software onto RPi, and control that via the standalone touch screen orbiters, that would be interesting as well.
Currently you are correct as far as i know. Phenigma's work on porting the full MD stack over to Rpi is seemingly the only option for lmce users currently (and I'm not implying its a bad option at all - by all accounts he's done incredible work).
In the future that may change. Whats missing in lmce today is all the Core side code to support upnp player devices. That's a fairly big chunk of code. Also our Raspbmc-CEC firmware image has Dianemo specific packages that implement the Dianemo CEC controller device, and those packages would need updating somewhat.
Basically what we have today in the Raspbmc-CEC firmware is something between an MD and a media player. Raspbmc does the media playback (and is 100% a standard build) and can be interacted with via upnp and via CEC. It plays that role very well indeed. The Dianemo-CEC packages, installed as part of the Raspbmc-CEC firmware, provide a Dianemo style device on the Rpi that allows the Core to interact with the local HDMI-CEC devices (principally your TV currently). So in the future we may add more Dianemo devices to the Rpi Raspbmc-CEC firmware that allow the Rpi to control/interact with other kinds of local hardware. In this way you can see that from a control perspective we will end up with something that delivers all of the local device control functionality that a full MD delivers. The functional part that is missing is the on-screen Orbiter UI and standard MD media playback functionality - that is replaced with xbmc. So principally what you loose is the ability to display the MD UI on the TV.
All the best