New rumors suggest that both the Canon 5D Mark IV and the 1D X Mark II will be announced early in 2015 (in the Jan/Feb time frame). The Canon 5D Mark III was announced in March 2012, while the 1D X was announced in October 2011. As such, early next year would be a fitting replacement time frame for both cameras.
The 1D X Mark II is rumored to be the first of the two announced – with the possibility that it could be announced late 2014 and availability in 2015.
Both cameras are rumored to include “significant advances in sensor design” and some of those advances we could see in the rumored Canon 7D Mark II.
Expect to hear more on this in the coming months.