The third edition will have an implementation of his paper on layered materials. There won't be anything on Manifold Exploration though, as pbrt has Kelemen sty

The third edition will have an implementation of his paper on layered materials. There won't be anything on Manifold Exploration though, as pbrt has Kelemen style MLT (the third edition extends it with Hachisuka's Multiplexed MLT) instead of Veach style MLT. They've added other cool new stuff too, such as volumetric path tracing, progressive photon mapping, hair (bezier curves with a Kaijya-Kay BSDF) and a Photon Beam Diffusion BSSRDF.