Thank you for the detailed answer. This is an interesting engineering problem.

I wish I had more free time, a gearbox or a 4-way differential can probably be used on the extruder head to control the mixing ratios.

Regarding the necessary research, I can picture it being cracked either by hobbyists, or industrial-scale (patent-heavy) players. I imagine that consumer-facing players such as Prusa do not have the means to heavily invest in R&D.