This took quite a while to get my head around.
Finally i added LabPBR shader support via specular maps.

I used LabPBR Material Standard) as a preset for the specular maps and build on it.

Actual values used - if someone is interested - can be found here.
// Note that it highly depends on the shader and their LabPBR settings

Currently specular maps are supported for all textures with multiple variants.

Added:

• LabPBR Shader support // for all existing "multiple variants"

Fixed:

• RP won't load due to unsupported characters in filename // removed filename colors