This is focused on the illuminant, treating the surfaces as having a spectral response that’s simply a per-frequency multiplicative factor. But to me the more interesting part of spectral rendering is being able to deal with surfaces that are non-trivial functions of the incident illumination, like phosphorescence/day-glo effects, where energy incident at one wavelength is re-emitted at a different one. It’s quite hard to capture this accurately in anything based on RGB.