Hi Tom, an external material format has always been planned, but as usual I like to wait until something has become quite necessary to implement, in order to have as clear a view as possible when approaching the design. The format can be made with or without an external editor, and I’m neither strongly for nor against building one of those — however it ends up, a plugin will be able to read & write the files, so an external editor would be optional to use, and my main argument against building one would just be that it would take time better spent elsewhere, without much of a payoff.
Regarding PBR in Rhino, it should be working, but I have fixed (internally here) a few issues with identifying textures in some cases, so you might try a few different texture sets from https://cc0textures.com to check whether it is just the naming used in the particular sets you have tried. And if so, and if it is convenient, I’d much appreciate getting a look at one of those failing ones, to confirm that my current code is handling them well.
Regarding your comment about not seeing where Rhino ends and Bella starts, I think I’d like to hear more what you mean here. I suppose it may be things like wondering if you can use a Rhino texture in a Bella material?
If so, you generally can, but you should usually prefer to use Bella textures, since the Rhino ones have to be baked to file to be used. I asked, and Andy open-sourced the logic for Rhino procedurals, so when I get time I will be implementing those directly in Bella, and this will mean we will no longer have to bake them to files.
Aside from that, it is still generally possible to use Rhino materials in Bella, and there can be arguments for that (e.g. using a single setup for multiple renderers), but the Bella materials will give you more direct control without the need for us to make a generally-imperfect translation from Rhino to Bella.
Not sure if this helps, so if you want to elaborate a bit, please do.