GumBall Model by Fabio Sciedlarczyk

Lama is a state of the art material layering system developed at Industrial Light & Magic that introduces a modular approach to building material networks and includes recent shading R&D work on energy conservation and dispersion.

Lama is battle-tested and in daily use at ILM.

Lama node composition also offers a simpler built-in mechanism for energy conservation and other properties, because of its fundamental focus on layering of physically based responses.

While Lama does not bring MaterialX support to RenderMan, you can define the Lama nodes as a series of MaterialX primitives.  See the MaterialX documentation for details.

You now have the very best of both worlds, being able to mix Lama and PxrSurface materials on the same asset, allowing you to mix and match to your creative shading requirements.