A report over at Northlight mentions testing of the EOS 5D Mark IV.
There is still a mix between 18 and 24MP. 24MP is the likely final outcome, with the lower MP sensor testing AF speed and buffer management issues (less than 8FPS is the likely shooting speed).
We've heard recently that the camera is coming in 2016, with shipping of the C300 Mark II and EOS-1D X Mark II to happen before the EOS 5D Mark IV. There's a lot of R&D dollars going into the 5D4 project, with the hopes of launching a product that is perceived to be a big jump in features and performance over the more-than-capable EOS 5D Mark III.