Assuming this rumor is true, I'd think Canon would still wait a couple of years before releasing it. Everyone that would buy a camera like this just bought a D800/e or Canon 5D III; and if you're a professional you purchased two or three of them. It will be at least three years before I consider purchasing another camera.
Everyone?? I see a lot of 5D II owners like myself that are not pushed to go to a 5DIII at all. And put off by the pain of starting a Nikon lenses collection. 5K for a camera along these lines would cost the same as a D800 and a 14-24mm lens and I'd be back to using my Canon 14mm L, 17mm TSE L, 24mm TSE L, and 24mm 1.4 L for architecture and landscape. Sign me up!
There are a few possible approaches to take.
1) Recognise that actually owning camera equipment is not very worthwhile unless it is making you money and/or you're using it regularly and then when you need it, rent/hire whatever happens to be the latest/best.
1a) Start up a Nikon lens collection, whilst keeping your Canon lens collection and just rent whatever body happens to be the latest/best/to your liking.
2) Build up an array of Nikon lenses, along with a D800 whilst keeping the Canon gear. Treat the bodies as something that can be sold/traded/whatever. Then you simply sell your older body and buy the new one whenever one manufacturer makes a big leap over the other.
Thank you, there are yet more...
(by the way, 1 is a non sequitur - whether anything is worthwhile or not is a subjective judgement that does not necessarily lead exclusively to the conclusion you offer) For example, my 1932 Leica sits on the shelf and looks beautiful but makes no money and is rarely used. Yet I find it very worthwhile.
3) live with my 5D II and my excellent collection of Canon lenses, don't be a part of the consumerist imperative and thus contribute to both corporations' bottom line, and wait for a camera that gives me improved results with the lenses I have. I am making money with the 5D II and can stick with it unless Canon provides something that will give me better results. Withholding my capital until then is the best strategy from my point of view.
also 1 assumes that photography is seen as a profession rather than a hobby
a generalised version of 3 might be that some owners sit on their hands and wallets until they are convinced that it is a good time to upgrade. These are the people that are the late users who wait until the technology is proven and the bugs have been sorted.
A good example of this from the Canon world might be the flash issues on the 5DIII where the 3rd party triggers dont work with HSS, or going back in time - the 1D3 AF problem