Well I have just had a play with the new 1DX MK3 and I personally like it!
I'm not going to review it, but also, as there is no software currently out to access the Raws, it stops there. However, what I will say is this, notice any difference in weight, NO. Yes, I feel there are some good step changes, but we all look at our gear in may different ways and what suits one, may no suit another. Please don't buy it on spec, you need to see it and try it before committing, as you may find that the MK2 is better suited and you don't require all the 'bells & Whistles' and I for one will use the video part very infrequently.
Unless you are a person like Arash who soaks up all the technical aspects of the camera and what it can deliver :S3: then seriously if you purchase it then I would strongly advise you take a Canon day and get to know your camera, what it can do, how things work and then Customise it to you and your 'style' of shooting, in that way you will get the best from it. As the Canon guy said to me first off, he read the manual several times, but only when out in the field did it come into it's own.
Cases well that is limited now to four, with 'auto point switching' buried elsewhere, but this now has limited options. Clarity slider, oh a bear trap IMHO, that will be set to zero/disabled for me, but some folk I think will get drawn into that!!! AF-ON button, that can be found in to places for Landscape or Portrait shooting, certain I will have the sensitivity turned down to zero, but what I would suggest is that the grip when not shooting in Portarait, that the button is set to disabled and have that in My Settings when you wish to enable it, because you could knock it and move the FP to a different position my mistake. Finally, if you found that when taking a card out it defaulted to the other, (frustrating I found with the MK2) you can customise that too, albeit a very small feature, but a handy one for me, but not one that may part you from $6500.
Although I will see it again next Friday, I doubt I will have as much one to one as I did this morning.