POST FOR DANKY
JLV please could you add support for control over the 'gloss' amount when importing content for mxs, ideally in texture map form to create more complex materials but even an add on to the current export script to include the slider value would be a dramatic improvement still using the old version of blender for exporting though the new one is the same - i think gloss is replaced by roughness in 2.8+
Currently when exporting any material with the mirror/metallic checkbox ticked you can add a visible reflection, but with no control over the hardness of this reflection you are very limited in the amount of materials you replicate convicingly. i don't understand shaders too well & i'm not sure if the current shader will support doing it the 'proper' way but adding a blur to the environment reflection based on the 'gloss' slider value would be the most simple version i can think of
this picture shows it well, currently we're limited to the materials with green outline when mirror is unchecked, and the ones outlined in blue when mirror is checked - the only way i have found to mimic roughness is to overlay noise on the normal map but if you do so on a small uv space the reflection is severely distorted
it's explained in depth here, i didn't get too far in but the concept of roughness is the main thing https://learnopengl.com/PBR/Theory