2009 is a possibility
I've been told from two sources that a 1D Mark IIIn is a definite possibility. Most people at Canon feel the AF system is fine, as does a large percentage of owners. An improved LCD, Buffer and possibly a movie mode could be added to the 1D3n.
I was told there was a newspaper that ordered 20+ 1D3 bodies and attempted to cancel the order at the height of the AF controversy. Canon shipped them 1/3 of the order to test the cameras out. A month later the newspaper requested the rest of the order and called them the “best cameras it had ever owned”. The camera has also been selling very well for the last 6-8 months.
Why no 1D4?!
As been talked about in the past, there is a murmur that Canon could be merging the EOS-1 line in Q4 2010. The motivation to lower production costs by manufacturing one camera. I think most people would agree it would be a good move. I'm not sure exactly how much money Canon could save having one body.
I know some people are thinking it, I've never been sent any credible information about such a camera.