I purchased a 5D3 early last year and kept my existing 7D. While the 5D3 gets used for most purposes, the 7D is still useful to me when traveling to destinations where both landscape and wildlife will be a focus. I can leave the 100-400L mounted on the 7D for wildlife, and use teh 5D3 for everything else. This saves a lot of lens swaps, plus I am ready for any type of shot.
The combination was very useful on a trip to Glacier National Park this summer. Quite often I hiked with both cameras, and could easily switch from landscape to wildlife without any delay. Wildife rarely waits for you to change lenses.



