Bake Metallic and Specular values / maps

currently, when baking, several properties cannot be baked out.

here is an image of what i know can be baked (green), and cannot be baked (red):

there are 2 application examples when these additional channels would be helpful:

• when baking procedral materials to textures, to improve performance or export. (replacing a complicated node setup, which would go into these channels with an image texture)
• when baking from an object with multiple materials to a joined object/material

having these additional options would allow:

• to create procedural materials, and export them as textures into other programs or engines (unity/unreal etc. need metalness maps).
• create single-material proxies of objects with many different material, to improve performance.

now, i know, these can be baked by hand, if you reconnect the nodes into the output, and bake a combined pass. however, this is not practical when multiple materials need to be baked. going through many materials and changing the node setup each time you bake is not a viable workflow.