The gradient map works only on the selected layer and is by that fairly limited in application. What would be really nice is if the gradient map feature was also available as a filter layer/mask option. That way, we would be able to use layer blending modes, opacity, make use of it in groups and so on.

An example of what I'm thinking about: An effect I've been able to pull off in other software and can be mostly accomplished in Krita is to set a base layer where you paint in most any color (but best in grayscale). Above that layer, there's a fill later with a pixel checkerboard pattern set to a blend option like soft light and dialed down somewhat in opacity. Set up a filter later right above that to posterize the image. What you get is a nice pixel-art result complete with dithering. Being able to set a gradient map on top of that non-destructively would allow you to continue working on the base layer with the full suite of tools available to you while still seeing the pixel-art result in the intended colors.

Well, the reason gradient map only works as it does now is because of bugs we keep bumping into. The latest bug was an issue with storing the gradient into the file in a way so that Krita would always know what type of gradient is stored in the kra. If it couldn't find the gradient it would crash, and fixing it required a significant bit of code to be written, so hence it was disabled as a filter layer for the 3.0 series.

I wrote that bit of code a few months ago, so the latest 4.0 build should have that, but it hasn't been tested much yet.

Awesome

I always had thought gradient map filter wouldn't work as a filter mask/layer is because of why pixelize wouldn't work as a filter mask/layer, but glad to see I'm wrong and it'll happen.