First I want to say I love working with the new PBR material features, and I'm not quite sure how hard this would be to implement since I realize that PBR Materials have standards that needs to be followed, but I would love to see an extra texture box when editing a PBR material that will override the metallic layer and tint the gloss on the object.
With the current implementation of PBR we are stuck with a grayscale metallic channel baked into the ORM, with no further possibility of tinting. If we compare this to the older Blinn-Phong materials, then we had a specular texture (which could have multiple colors) and a sepparate tinting channel.
Having the ability to color and/or tint the gloss on an object, like we could with the old Blinn-Phong materials, allowed for the creating of very interesting objects that had an irridicent shine, having one color on the actual base texture and shining in a different color. This would be similar to mother of peal or certain car-paints that change color depending on angle of the light.
Due to the current implementation of PBR with the metallic/gloss layer baked into the ORM these kinds of shifting gloss materials are no longer possible to create when PBR is active.