I've seen this mentioned here and there for pixel art and what not, but I wasn't really clear on whether you were considering this for Krita. Will we be supporting a color-replacer brush/filter, or better, a gradient map filter? (Basically, replacing with a custom gradient respective to the value percent of each pixel.)
The fact that you can paint using filters as it is, and paint using gradients, this would be so much cooler than in PS. (And I only mention PS because it's a feature I tend to use frequently.)

My use case is more to the tune of grayscale painting, then coloring; and the color mapping from grayscale using normal filters is dodgy at best when working with different colors.
Or is there another way I can make this work?

Thanks!

its a popular wishbug, one that i think i've voted on.

https://bugs.kde.org/show_bug.cgi?id=335405

Would be a good candidate for a future KS.