The release dates will depend on the technical challenges and not just the release schedule of previous cameras.
For the R5ii, the rolling shutter would need to be improved for the next version, and that might not be easy to implement in a 45MP sensor. I would think that the R5ii would also feature dual CFe-B cards since the price of those cards has come down significantly.
The A75 would most likely upgrade to the 8-stop IBIS in the A7R5 and could also implement full width 4K60 to compete with the R6ii. Such a camera could take away sales from the A7S4 though, so maybe they would release the A7S4 first. I expect the A7S4 would have some features to justify the extra cost over the A75 though, such as 4K120 and internal ProRes recording.
Just my thoughts.