The topic isn't Solaris specific, but because of how it can be implemented - esp. in Houdini - seems to fit here best.

I'd like to hear people's thoughts on why an asset would need different materials vs. a single one, when most (/all) aspects of the shader can be controlled by textures. Additionally - with primvars - the material can be further diversified (modifiers in the shading networks eg. color corrections of the textures driven by primvars), even the texture paths could be read from a primvar - so that pieces of the asset get different textures.

Only one material per asset/scene is of course an extreme case and I'm aware for things like skin, hair, ... - highly bespoke materials - you'd want a specific shader. But I'd like to get people's thoughs on the other 90%.

go for it

Nothings really stopping you from trying and I believe its not uncommon to minimze the number of materials in realtime applications. The main downsides I can think of are i) textures and primvars are generally more work to with deal compared to sliders on a material and ii) reuse would be more difficult since it's harder to extract the look into some kind of library.

From experience, It's much easier to resurrect an old asset that has an xml or something that lists what materials are assigned to what prims. It also means you don't have to debug a monolithic single material to only fix a small part of it (and deal with a potential knock-on effect in other areas of the material). Compartmentalization is your friend in that scenario.

In your example use case, you would need to somehow record/store/assetize all the info of all primvar-driven texture adjustments which sounds like a pain.