Hamed Zaghaghi has been developing these features and they're currently being reviewed by Ton. The results look very promising.
Finally it's done, sun and sky. The patch is uploaded but only for review. Ton want that I moved sun settings to Lamps, then we can add more than one sun into the scene. BTW, test the patch and if you made some nice pics you can email me to paste it here.
You can get more details, here.
Note: Downloading the patch file will not allow you to test these features. The patch must be compiled into a build of Blender. Hopefully, someone will create a build that has these features so they can be further tested. This will most likely be made available by the dedicated folks at graphicall.org.