Great to hear about clearcoat! During refactor do you consider adding ggx/multiscatter ggx info fresnel node: Cycles Requests - #450 by Eneen or maybe even separate clearcoat node with absorption?
I’m asking about multiscatter because of metals.
From https://blog.selfshadow.com/publications/turquin/ms_comp_final.pdf (I’m not sure if this rafactor is based on this paper, correct me if I’m wrong):
The most notable difference is the amount of saturation on con-
ductors, with the reference looking slightly more saturated at high
roughnesses, even with us using Fms of Eq. 15, rather than the more
justified one of Eq. 12, that saturates the result a bit less (Fig. 7 left)
I guess without multiscatter current workaround for proper conductor node (patch: ⚙ D2003 Cycles: Add a new Metallic BSDF, combining condictive fresnel and multi-scattering GGX) will not work: GPU Compatible Thin-Film Interference v2.1: Glass Within Glass + Absorption - Materials and Textures - Blender Artists Community
This nodetree uses glossy node with multiscatter ggx.
But maybe multi will only disappear from principled but not glossy node?
What I’m trying to say is that conductors and coated dielectrics are not perfect (no spectral rendering), but taking multiscatter away would limit them further. I’m not jewellery guy but having good metals or coated glass for archviz is IHMO common thing.
Hope this combined info is somehow helpful to you.