This has been around for a few years now, but it is doomed by a non-commerical/restrictive license.
https://krita-artists.org/t/implementing-mixbox-mixing-for-k...
https://krita-artists.org/t/implementing-mixbox-mixing-for-k...
https://invent.kde.org/graphics/krita/-/merge_requests/1783 https://krita-artists.org/t/can-we-get-mixbox-on-krita/64201...
GPLv3 reimplementation linked in that thread: https://github.com/joeedh/pigment-painter
MyPaint also has it though, and that's open source: https://mypaint.app/blog/2019/01/26/MyPaint-2.0-alpha/ (https://github.com/mypaint/libmypaint/pull/56 mentions using 7 primaries for blending), and another older thread about other methods: https://community.mypaint.app/t/real-color-blending-wip/390 . MyPaint IIUC is integrated into Gimp, so I assume Gimp can also do it using the MyPaint brush engine.
Edit: I was responding to TFA's claim "there was no practical way to implement true pigment mixing into digital painting. Until now." but this page isn't dated - seeing how many other discussions reference MixBox blending could this need a [20XX] tag? I don't think it's new.
The algorithm could be patented, I guess, but it doesn't seem to be.
The algorithm is not the natural phenomenon of pigment mixing. It is about how to mix RGB values in a way that imitates natural pigment mixing, which is not something natural as nature doesn't work in RGB.
https://github.com/scrtwpns/mixbox/blob/master/cpp/mixbox.cp...
Like, it looks like just decompress that lut and have it decompressed in the project and the rest is just interpolation algorithms.