Doing more and more music and audio for film/TV, I'd love to see a dedicated output driver (or something) where I can set up a viewing room with Sonar feeding the video and audio playback directly.
 
Perhaps something that integrates with the Western Digital media players (TV Live) or similar. Perhaps something that outputs to optional video cards... Not sure what is doable, but I think that would be a really nice feature.

It would save time in not having to render the video first, and one can make adjustments on the fly with the client sitting there.
 
And while you're at it... a 5.1 option would be nice too :O)