It seems clear that Nikon should have released a D700x, but I disagree about the D3x being a failure.
It did sell well for many years, was a much superior camera compared to its main competitor, the 1Ds3, and simply redefined our expectations in terms of DR. While expensive it was competing performancewise with MF backs costing twice as much.
How do you know that it sold well? I never saw statistics by camera manufacturer and model of their cameras, but maybe I missed something. When you say it's much superior than the 1Ds mkIII it's really only DR that is better. Since I have a 1Ds mkIII I looked at comparative D3X RAW files from e.g. Imaging Resource. And quite frankly I didn't see much difference in IQ worth speaking of. Certainly not anything of a magnitude one would switch systems for. When you say teh D3X competed against MF backs costing twice as much, which would you compare to? I think the most relevant comparison would be against the Pentax 645D and IQ wise I don't see the D3X in the same league. And the price for the body was about the same.
It's interesting to note that I have not seen any reviews of the 5D mkII when it came out that predicted the success it has had! The 1Ds mkIII from what I sense has sold well too, but the success was the 5D mkII which was better in a few areas compared to the 1Ds mkIII but in most areas a lesser camera. Live view for landscape photographers and architecture was a very strong point of the 5D mkII with nothing else on the market comparable at the time.
In terms of system, the 17mm T/S, a very niche product, is probably the only lens in Canon's line up that delivers something the Nikkor really cannot do. For the rest we are talking about tiny differences with one brand topping the other in one direction or opposite. Nikon is rumored to release a 17mm T/S soon following the publication of a patent. Considering the overall domination they have in wide angle technology, there is no reason to think it will not be best in class.
It's not only the TS-E 17mm but also the 24mm that Nikon does not have a competitor to. Also the Canon 70-200 f/4L IS has no Nikon equivalent. But notice that Canon has upgraded a huge part of the lens base in the recent couple of years. They have got also extremely expensive, but the new lenses are really state of the art in the format. All the long lenses and TC's have been updated. The Canon 70-200 f/2.8L IS II is the best f/2.8 in class and I would be surprised of the new 24-70 f/2.8L II would be similarly good. I think it is fair to say that Canon has the lead here.
So I don't think it is so obvious which system is the best at the moment. Clearly the D800 and D800E is attractive from the pure resolution and DR point of and nothing else. In fact there are several shortcomings compared to the 5D mkIII like memory settings (C1, C2 C3 on the Canon) and live view imprementation. AF might be the same quality. The speed in continuous shooting is clearly better on the Canon.
I know this might sound as coming from a fan boy
but really I like to have things put in perspective and I find many post about the D800 to be a bit over the top quite frankly.