I wonder if there is a design benefit for longer lenses to switching the position of the zoom and focus rings. The position of the rings on the 70-300L could become the new normal.
I'm not sure. The zoom ring is also further out on the 200-400, but that might be so the hand on the lens is close to the zoom ring (that hand will be further out on such a heavy lens).
I had assumed it was the target market - Canon's 'lens positioning article' suggested the lens was aimed at APS-C shooters (and 'of course, it also works on FF cameras), and the 70-300L is similar to the high-end EF-S standard zooms. FWIW, the zoom ring is in back (opposite of the 70-300L) on the other 70-300 lenses (non-L and DO).