I would agree with the notion that a 5D Mark III would not hurt D sales if the Rumor of NO 4K video is correct in the D5 mk III. Many will, if they can, shell out extra $ for the 4K video option. If the previous interview with Canon Executive holds, 4K needs the body space (currently) of a D body, and I would add to not affect the still picture specs of said camera. He also mention more specialized body's, so 4K D5 may be an future option along side a High ISO model.
I also agree with the comments about being "Vested" in a brand system. Smart money goes into lenses, so when you do upgrade a body, you want it to be worth the cost. That and Canon's currently long lapse time has created some high expectations here, and I too hope they bring some BOOM with the flagships!