I have quite a lot invested in the Canon system and I have been shooting it for years. The last body I bought though was the 5D Mark II. I recently decided to test the Nikon waters with the D810, 14-24mm, and Sigma 50 art. I've been pretty blown away with the D810. After a few days of utter confusion, I find I like the interface far better than Canon. Things just make more sense and you don't need to go into menu's all the time. The features and image quality are a really big jump from the Mark II.
I was using the Magic Lantern, but that to me is an absolutely horrible user interface and I really hated having to use it. I want to concentrate on the image and not be fiddling in menus all the time.
On this announcement, I suspected Canon wouldn't make any dynamic range strides (or possibly make things worse), but was hoping for a suprise. I still have all my Canon gear, and I think Canon has the best lens lineup. I have so much invested in Canon glass..... Perhaps I will shoot two systems and try and use the strengths of each. Perhaps Sony will come out with a professional level mirrorless camera and I will go the route of using a Canon adapter. I imagine we are in for a multiyear wait for any future sensor innovation from Canon.