Northlight is reporting they've been told that the EOS 5D Mark IV isn't scheduled to be announced until the fall of 2015 at the earliest, and that we won't be seeing it until the EOS 5DS/5DS R are shipping in reasonable numbers. It was interesting that they also mentioned that current EOS 5D Mark III sales are still good and that may delay the release of the EOS 5D Mark IV until after the EOS-1D X Mark II is announced. It sounds like this has yet to be decided.
A separate report from Northlight says the EOS 5D Mark IV would have a 28mp sensor, 9fps and shoot 4K video. The camera would also see a “significant” advancement along with the EOS-1D X replacement in external flash control capabilities. This would include adaptors/controllers and firmware updates for the latest Canon DSLRs.