Sure a lot of things can be worked out but it takes a ton of work. You probably remember the discussion from Hardmode - Manually Mix Colors where realistic color mixing is discussed and the issues there are. You will have this in addition to the whole material simulation. That’s quite a lot. Having an external program, sort of as a plug-in, could kinda outsource the issues to another program but this program as well has to exist and allow the mode of operation you described i.e running as a background process that can communicate with other processes. It’s not trivial. I could think of a lot of plot stoppers and I think the Krita devs can think of even more.
However since Krita is open source, there is always place for hope that someone who is realy into this topic and has a solution will add their part.