I think it is a pretty good guess that the R7 outsells the R5 in numbers, so a more capable R7 should sell well, but there is the question of how much better. If Canon were to do the full deal with 40MP and a stacked sensor, then we are talking R6 II price point or even higher and that would sharply diminish the number of R7s sold. Money really matters, particularly with APS-C and in these financial times. Clearly, the R7 was a compromise between a 90d and a would-be 7D III and the price point is quite aggressive for what you get. By all accounts, the choice was a good one, because there are a lot of folks shooting with an R7.
The advantage of an 80-100 MP FF for moving creatures is not image quality, but rather likelihood of capturing the target. The wider field of view and wider AF window are significant if you are shooting FF with the same pixel density as APS-c. The high MP FF is also attractive to landscape and architectural photographers, so it has the potential for a move diverse customer base than an expensive R7, but the inevitable price point would still shrink the available market. For the moment, I am holding on to my R5 and watching the R5 II. I would immediately upgrade the R7 for either of the above choices and notably, adding an R5s would not cause me to sell my R5. Interestingly, 100.7 MP is the break point for 12k video and that would be something else to talk about and would potentially add another market segment.
If I had to put down a bet, I would bet we will see an R5s in the same time frame as the new Tilt-Shift lenses. My sense is that a full-house R7 any time soon is unlikely, both because of the history of the 7 series and the market shrinkage the higher price point would cause.