Interesting question, for which there is no single good answer. It's like when I get asked by family or friends - what camera do you recommend? The answer clearly depends upon 'what do you want to do with it and how much do you want to spend?"
Since the second part of the question is moot here (cost not being an issue), the answer then must depend on what one is going to do with it. The responses here so far have again highlighted people's own personal preferences (and perhaps prejudices).
There is no SINGLE camera/lens combo that will serve all the needs of most photographers, certainly not mine.
My first love is wildlife, including action shots. Although not so much into close-up portraits, I still need a longish zoom for animals on the African plains and the camera has to be capable of rapid AF and fast frame rate - at least 8 fps.
Second love is landscapes and nature. Need a relatively high resolution sensor, with a wide angle lens on it that is also capable of night photography.
I also like travel photography and sometimes the wife insists I take family portraits too
No way a single body/lens can fit the bill.
Hypothetically though, if I had to choose just one, I would go with the
Canon 1DX with the 28-300 f3.5-5.6L combo.
Yes, tame it is, but the 1DX is probably the best wildlife camera out there, with its superb AF, up to 14fps capability and full weather sealing. The images out of it are some of the most natural I have seen, where animals are concerned.
The lens is a compromise, sure, but gets me the long zoom, and at the wide angle I can probably stitch verticals for a pano style image. Yes, it is too slow for northern lights but that's one thing I will have to live with. Not as sharp as the 24-70 MkII or 70-200 2.8 but still very good for the range it covers.
There you have it. One camera, one lens for both wildlife and nature. Since I don't do fashion/street stuff, the size/heft of the combo would not bother me. Heck it would even work for people and family portraits for holidays and all that. Given the huge bags people carry these days, it might even work for travel with the zoom on it without attracting too much attention.