A little more analysis:
The time between 1D and 1Ds releases shows us a full-frame high-end camera will likely be released in mid 2011
Shortest time from 1D->1Ds is the Mark III (179 days)
Mark II (236 days)
Longest time from 1D->1Ds is the Mark I (364 days)
Based on that and the release date of the 1D Mark IV the next in line should be announced between April 17 and October 19 2011.
I think 2011 will bring replacements for (in chronological order):
Rebel XS replacment (12MP, 720p video, ISO 3200 max)
7D Mark II
1Ds Mark IV
T2i replacement (entry-level 7D Mark II specs)
Based on existing trends I don't think Canon will release a 5D Mark III with specs similar to 1Ds Mark IV until 2012. That doesn't mean that Canon could buck the trend a release a different enthusiast FF camera in 2011.