According to Canonrumors that Canon 6D Mark II ready to debut, but not this year. They will announce this camera after the starting market selling of Canon 5D Mark IV. The 5D Mark IV expected selling time to be around first quarter of 2016. So, the Canon 6D Mark II will launch in early 2016.
(Also see Canon 5D Mark IV Rumors)
This prediction time is based on the way that worked to turn Canon announced the 5D Mark I and 6D before. The Canon 6D Mark II rumors, will have a smaller body and a bit lighter than the previous version, does not use old LP-E6 / E6n batteries to reduce the weight of the body, Full-frame CMOS sensor with a higher number of megapixels, but not above 24-megapixels. The Canon EOS 6D Mark II will have its own sensor same as the Canon EOS 6D.