Check out my water spreadsheet

[qmax]

This linear fit seems solid, I doubt it will deviate much even at 70°C, although it would not hurt to verify.
Now if we find that buffering capacity does not change appreciably with temperature, that would be enough to predict mash pH at any temperature.

We will probably need to look at the titration curve at different temperatures and see from there which coefficients may need modification and what could be done.

If buffering capacity doesn't change, the only thing we would additionally need to know is the glide coefficient for every (base) malt.

Then we will be able to establish a common denominator for malts with vastly differing glides like Munton's.
Also that may improve our understanding of the desired target pH.

I'm interested in it certainly but I expect that many will conclude that an occasional mash pH at room temperature is a sufficient quality control measure. That is, after all, what most breweries that do mash pH checks, do.
My efforts are aimed at seeing whether we can improve the value of that proxy.
It is on validity of re-referenced mash pH that I must now focus my attention.

Well, yes. Beer is beer is beer, and it was brewed for many centuries without any pH measurements.
It just depends on how you look at it, but I think there is still room for improvement.