I haven't read all posts here but I saw you acknowledge that any work that requires heavy cropping benefits from such a sensor. In that post, you also dismissed that, since a crop body would suite that use case even better. But I don't think that captures the whole picture. If you do reach limited photography as well as regular one, getting one body that performs well in both instead of two specialized ones may be worth it.
With either electronic shutters getting even faster (Like in the Sony A1) or global shutters emerging, the only advantage of a crop body becomes sensor price (+ size and weight, if Canon develops a special crop RF lens lineup). With the speed of current electronic shutters from Canon, FPS would remain an advantage. But I think it is fair to assume that will faint in the future.
So a FF body with 2.56 times the resolution of a crop body is a straight superset of it. For it to make sense to buy a regular FF body and the crop body, the high resolution camera must cost more than the sum of the two. So the premium you pay for the high resolution has to be greater than the cost of a whole crop camera for it to make sense to get two bodies, instead of one to do it all.
As to moving to a larger sensor format in the pursuit for higher resolution, one may already have an EF or RF lens collection, that's holding you back. And don't the typical drawbacks like cost and lesser technology still apply to these bodies?
I think with most specs you will not find an actual need for them anymore, with the exception of few very special use cases. But there's a desire for more MP, more FPS, more video resolution, etc. Having and not needing something is better than needing and not having it.