About your question about IOR, we don’t have at this time such control in conductors, but you can set up with frontal reflectance and it will be automatically generating the IOR. We have been considering to allow a direct control over that, but we always start by exposing fewer parameters, and adding more only if needed.
Also, I want to mention we don’t have additive control. That’s one of the purposes of having layer system, for example to create a plastic you have a pick a diffuse conductor substrate, and you can add a glossy or specular layer above it with IOR 1.2 for example. So you don’t need to deal with additives that can end having exceeding energy problems, and this layered system have not.
At same time we will add more layers, to allow for example “clearcoat”. In the meantime you can use blending material to mix multiple materials.