Northlight has posted a bit of a roadmap for the pro level cameras from Canon. They've been told that the EOS-1D X Mark II would come first, with a potential announcement coming in very late 2014. The EOS 5D Mark III would follow afterwards. Both cameras will most likely benefit from the new sensor technology we'll see in the upcoming EOS 7D replacement.
If the technology in the EOS 7D replacement is as great as people are claiming it to be (we don't yet know what it is), then it would make sense to replace the other flagship models in the lineup fairly quickly. The EOS 5D Mark III was arrived in March of 2012, and the EOS-1D X soon after in June of 2012. A three year cycle for each seems doable, even if the EOS 7D will have taken nearly 5 years to replace.