@eugenialoli Hi - I am late building a working GIMP 3 build environment on my computer - But I checked the functionality online -
Yes, it is a matter of building a GEGL plugin targeting the appropriate channels. Once one is more or less proficient in it, it should take a couple of hours (I am not, yet) ,I don't think layer effects in GIMP 3 can be individually masked, though - the workaround for that is having a layer copy, with a mask, and apply the effect on that.