We've been told by a couple of people that the Cinema EOS C300 will be replaced in time for NAB 2015 in Las Vegas this coming April. The Mark II version of the C300 will indeed be 4K, which I think would have been assumed, though you never know with Canon. We're told there will also be a “bunch of other improvements”, but what those additional improvements would be wasn't specified. I suspect the C300 Mark II is going to be a bigger upgrade than the C100 Mark II was to the original C100.
We're also told there will be some kind of an announcement for an over the shoulder style Cinema EOS camera to compete directly with Alexa. The hope is for that camera to be ready for NAB, but it could come after.