The EOS 5D Mark IV received a mention recently as possibly being announced in early 2015. One of the features mentioned as a possibility is 4K video capture. Although, I'm pretty sure every future Canon DSLR is going to be rumored to shoot 4K video.
If the EOS 5D Mark IV is coming in early 2015 as this rumor suggests, then I cannot see 4K being a part of the feature set. I don't think we'll see 4K video recording in a “prosumer” level DSLR from Canon until the technology moves down the Cinema EOS line.
I asked someone in the know recently if Canon had market research on who buys the EOS 5D Mark III and for what purpose. I was told that the videographer focused purchaser of the EOS 5D Mark III was less than 10% of the total sales. The camera is, and has always been, for the still photographer.
If Canon wants to grow in cinema and 4K capture, and they do, then they have a whole new line of cameras that is one generation into its existence to add these and other features to at various price points.
My 2 cents anyway…. :)