We are likely to see Canon’s 1D X Mark III and Nikon D6 to be announced in Q4 of 2019 to Q2 of 2020. Just ahead of 2020 Summer Olympic games in Tokyo, Japan.
In addition we can clearly assume that Sony will also replace the a9 sports mirrorless camera for the Olympic games next year. This would probably be the Sony a9 Mark II. There were rumors floating around about the Nikon D6 for almost a year but the company focuses on the full frame mirrorless and skip the CES 2019 event earlier in 2019. So by the end of this year a possible update to these pro-grade cameras are expected.
On the sensor side the 36MP sensor is a FAST sensor with chip-on AF, perfect for sporting at high continuous shooting speeds. Sony will most likely use it on the Sony A9 II. We might see this one on both Canon 1D X Mark III and Nikon D6 as well.