I have seen the Canon EOS-1D X Mark III in all of its glory. A source sent me images of the new flagship Canon DSLR with the caveat that they'd be for my eyes only. I respect all sources wishes, so I will not be posting the images.
I can tell you what I have seen though.
Ergonomically the Canon EOS-1D X Mark III will be almost identical to the Canon EOS-1D X Mark II. The first visual difference is how all of the ports are laid out on the side of the camera, and there are also additional port covers. The N3 remote jack has been moved to the side below the headphone jack. The memory card door is also a different shape, unfortunately, I could not see what slots were behind it.
Other than that, everything looks about the same as the EOS-1D X Mark II, which makes sense. Why mess with a camera design that is pretty much perfect ergonomically?
We did not get any specifications at this time, but we have reached out for more information.
There are Canon announcements tonight, but for the moment we don't believe the EOS-1D X Mark III will be included in those announcements. Unless we get a development announcement.
If I get permission to post what I have seen, I will update this post.