this reminds me of Polyworld by Larry Yaeger, an artifical life sim where each creature has a vision system. i played around with this back in the early 2000s though the hardware i had access to was basically insufficient to run it in any real way. it's nice to see its development has continued.
i made some art on this site years ago. some people used this to make plottable art. plotting it is definitely a slower way to watch it work through a drawing :)
The main benefit I see is being able to more accurately represent different light sources. This applies to transmission but also reflectance.
sRGB and P3, what most displays show, by definition use the D65 illuminant, which approximates "midday sunlight in northern europe." So, when you render something indoors, either you are changing the RGB of the materials or the emissive RGB of the light source, or tonemapping the result, all of which can approximate other light sources to some extent. Spectral rendering allows you to better approximate these other light sources.
i would expect the more dense part to be the smaller gamut that can be made with paint since we've been naming those colors for a lot longer than the larger gamut that can be made with a screen. The paint/print gamut looks kinda like the more dense parts of these scatter plots within the larger sRGB cube (though the paint gamut isn't entirely contained within sRGB).
diffraction grating wouldnt give you a controlled lighting environment (illuminant). they seem to handle that issue here by using a known spectral reference chart which might let them handle any normal lighting environment.
i lived about a half mile from this house in the same neighborhood -- it could be a lot more expensive if it had the view some properties around there have.
https://en.wikipedia.org/wiki/Polyworld