It's very difficult to get reliable information about upcoming firmware unless it's part of a marketing strategy like we saw with the EOS 5D Mark II and EOS 7D.
There is always a firmware update for DSLRs and anything for the 6D Mark II is likely bug fixes, I don't recall a time image quality or that sort of thing was improved with a firmware update (feel free to correct me on this point).
I can't imagine a feature other than 4K and focus peaking people would want to see in the 6D Mark II, as it's definitely not short of features.
Firmware update to add a second SD slot or headphone jack?