Add PBR shader https://github.com/GameMakerDiscord/PBR_shader_GMS2
Why don't you start to publicly release testing versions (like minecraft snapshots)? I think the community will test and help with fixing bugs. It'll draw more attention to the Mine-Imator. Perhaps there will be those who will help with such a great deal of work.
Will the source code be posted on github?
My suggestion: Custom Render Settings on each models. It is convenient in a situation when you need a different AO or Glow size on different blocks.