In element graphs you can use a mesh paint mask input to direct certain inputs in an element graph, but you can only use it in the canvas viewport, not in the layering viewport.
Justification
Having the mesh painting mask direct features in an element graph directly in the layering window would potentially open the door for a plethora of brush painting effects in the layering workflow: Guiding rotation of guided scattering, using it for directional blur or warp to create smudging effects, controlling noise size etc etc.
Implementation Details
I don´t know the technical feasibility of this, the feedback in the canvas for the mesh painting node is quite good, but I don´t know if this would be possible in the layering viewport. If its too heavy, maybe add a “manual update” option to it, something that would only update AFTER each paint stroke, not on each “tick” of a brush stroke, or even only manually once you enable it.