Hi -- great little package (I found out about it via GameFromScratch, naturally!)
I'm using it to experiment with Unity with a view to devising some lecturers and tutorials on 3D graphics.
In my use case, the most obvious missing feature is the lack of ambient occlusion maps, and at the moment, I hack around it by passing my occlusion map to the roughness channel and renaming the file afterwards.
I realise that adding a dedicated occlusion map output node means more work as you have to reprogram the preview to show the effect, so perhaps instead you could add a name-your-own output option.
Obviously anything made with it wouldn't be visible in the preview, because the software wouldn't know what to do with it, but it would make the software compatible with a lot more material workflows, and effectively (partially!) future proof....