The 1 DX looks like a nice tool for pros who know what they need, but not a one for all camera. Photojournalists, wedding photogs, and sports shooters come to my mind as possible users.
Someone mentioned BIF: If one comes from an APS-H form factor, this may not be the right tool. It requires bigger, heavier and more expense lenses.
The FF will also be a challenge to many who have bought into crop sensor lenses, or who enjoy the sharpest center part of their FF lenses on a crop sensor.
About high ISO performance vs. megapixel count: The credit should go to Nikon with their D3 (and D3s).
Nothing has been said about live view. How does it focus using live view? Is it easy to use?
I would assume that 1DX has a good battery life, but how good? After all, there is a lot of processing going on in the camera.
I am one of those who wish there was a built-in GPS. WiFi would also be nice.
To sum it up: seems like a good tool for many applications, but pictures tell more than a 1000 words.