One of the first reviews of the new Canon EOS 1DX:
Except for the lack of AF at f8 (this really, really sucks when you want to use a 2x extender with an f4 lens like a 4/500 or 4/600 for birds), the Canon EOS 1DX seems be be an awesome camera.
18 Megapixels is enough even for landscape shots. Of course for really large prints, more pixels are better (like the 36 MP of the Nikon D800) but up to A2, 18 MP should be more than fine – when good (and expensive) – lenses are used.
And 12 frames per second is a dream for action photography like birds in flights, sports or even playing children, particularly with the new and apparently absolutely awesome AF system.
Of course an EOS 7D will give you many more pixels for distant animals but when you can get close enough, the EOS 1DX will have a much better image quality.
And the EOS 1DX will work much better at higher ISO settings than an EOS 7D.
I think the EOS 1DX + EOS 7D would make a fantastic combination for the bird and wildlife photographer and will also work very well for macro and landscape work.
If you shoot mostly landscapes, the EOS 5D III is probably the better option because it has 4 MP more and costs only about 50% of the EOS 1DX.
Canon will probably introduce another DSLR in the coming weeks because they always do before Photokina which is in September.