That way the light will refract on the internal boundary as if it moves from the one material to the other.

Prerequisite is that you ened to be able to create non-manifold objects...

https://blog.yiningkarlli.com/2019/05/nested-dielectrics.htm...

that inspired me to add the feature to my renderer (rayrender.net).

The downside to priority tracking (and possibly why PBRT does not include it) is it introduces a lots of overhead to ray traversal due to each ray needing to track a priority list. Modern raytracers use packets of rays for GPU/SIMD operations, and thus minimizing the ray size is extremely important to maximize throughput and minimize cache misses.

POV-ray supports all kind of ray tracing and path tracing techniques, not just Whitted RT.

The simplified history is usually presented as Whitted Raytracing -> Distributed Raytracing -> Path Tracing.

The gist is that in Whitted for each surface hit a single shadow ray per light, a reflection ray and a refraction ray are traced. Shadows and reflections are perfectly hard. Distributed raytracing takes all those single rays and shoots N randomized rays instead, which gives soft reflections and shadows. Neither of these orthodox algorithms imply indirect lighting, which is what Path Tracing added into the mix.

This is not considering other light transport algorithms such as radiosity or photon mapping, which were popular ways of doing more cost effective global illumination in the nineties and noughties.