A bunch of websites are claiming that Canon Germany confirmed that a successor to the EOS 5D will be announced at Photokina in Cologne during the last week of September. Since all these websites have predicted such a successor for quite a while, there's no reason to believe them now...or is there?
As far as I know, no one has published verifiable information as to what Canon is working on at this time, but my gut feel is that Canon will not allow Nikon take the lead with its recent products, including the D90 with its video capability.
While there are rumors that the 5D successor will be a 21.1 MP full-frame 5 frames per second machine, with LiveView and a 3.2" High Resolution Screen (LCD). However, I suspect that 21.1 MP is not reasonable as it would take away a very large chunk of market share from Canon's $8000 1Ds MkIII. I also happen to think that Canon may also feature a camera with video capability.
The Nikon D90's feature of recording cinematic-quality movie clips at up to 720p HD (1280 x 720 pixels) is an immense step in the right direction, and opens up all sorts of opportunities.
The merging of still and motion photography is what most photojournalists need to meet the industry's current challenges...and Canon will not let its supremacy slip away.
Wishful thinking? Perhaps.