I've thought about a similar thing but been too scared to mention it in case someone hits me! (virtually)
The way I was thinking was a port of the server and database components to Linux, so that JRiver can be installed on NAS's in a similar way to Twonky, Squeezeserver etc, to replace the many dismal attempts at a DLNA server that is bundled with such devices. This would have the huge advantage of not having to keep a separate power-hungry PC or Mac on all the time.
Bundled and free servers do not have the customisation facilities necessary for "serious" use, only allowing indexing by track artist, album and genre for example.
I'm not sure about such a port being able to render media as the OP has suggested to go the whole hog of competing with high-end music servers to the extent of supporting/providing hardware as well, what I'm suggesting is a DLNA server that simply serves the content directory and files and transcodes as necesssary, and you can mix and match to your own rendering and controlling software/hardware. If you want a high-end DAC then buy one! As long as it can act as a DLNA renderer.
I'm not sure how far advanced the DLNA market is yet though, TVs with DLNA built-in are certainly very patchy in their compatibility. And I'm not sure how much audiophile DLNA (non-proprietary) equipment there is as yet.
But JRiver MC has to be the most powerful and easily set-up DLNA server as yet (for example, I found Twonky, Squeeze and XBMC really difficult to set up and understand and they still can't index my collection the way I want it), get in there early lads and allow it to be installed on NAS's!