Yes, that link is the same scenerio like this.
The grayscale filter would be interesting in order to add layers like water in rainy days, snow in winter or flowers in spring…
With that jaggied borders the only utility may be for the procedural foliage (hidden masks+filter nearest).
My goal was to use 1 RGBCMYK for the base and up to 128 grayscale layers over, masked them for aditions like wearmaps, flowmaps, snow, erosion, deposits etc.
If I dont find a solution the only way will be using 2 x RGBCMYK splatmaps for a total of 14 layers.