To AERO BLUE: I too thought the split rear window would have been a highly recognizable "signature" for the XF, and would have been a cool "retro" idea. (but I'm an admirer of the '63 Vette and the DeTomaso Mangusta too) Then again, I've never actually had to live on a day to day basis with the visibility limitations that type of styling can cause. I suppose that's the biggest reason D/C chose to exclude that particular styling exercise from the production model.
Wasn't the show cars split windshield an "illusion" created by the use of a single large, center mounted wiper blade?