Ok, that helps a lot, but the idea is to give the artist the ability to paint vertex colors in order to change certain aspects of the model using a mask.
Example. Use the vertex color info as blending parametros to multiply a predifined mask by the roughness, in order to introduce variation throughout the level.
The shader i have in mind have the Base Color, a packed Metallic/Roughness/AO and a normal, plus a packed 512x512 mask (a different mask in each channel) used as a default (artist only can change uv tiling), and that mask multiply the other textures using the vertex color as blending information.
Does that make sense in virtue of your answero?
Thanks.