For the viewport, it would be nice if we could get color management, shadows, a little better transparency, perhaps the option of reflections and some form of GI even if they're not realtime but fill in like progressive rendering. If it could use the same shaders as the final render it would be useful.
For final rendering, perhaps some GPU help (similar to PantaRay). It seems it's not yet practical to do everything on the GPU but perhaps some things could be handed off like AO calculations, maybe area light shadows, and volume particle shaders. I'm not a programmer so I don't know how possible this is but shops like WETA seem to be doing it already so maybe that can trickle down to the average user at some point.
Anything that could accelerate the volume particle shader would be sooooo nice. I'm sitting here waiting for a preview right now so that's why I have time to type this
Just wishful thinking...
