You sound pretty authoritative here, so I'll ask a semi-topical question: are the creative teams the ones driving this kind of development? "We need better fidelity/IQ because I would like this film to look more impressive that previous ones." Or is it more along the lines of Pixar demonstrating industry leadership?
It's both. Each new movie will generate new technical challenges, and the tech side of the studio will be prompted to rise to the new creative demands. Finding Dory, for example, is a natural choice for using path tracing because of all the refractive surfaces-- In a movie that's set in the ocean, it's pretty important to have water that looks realistic and natural (and frankly, using older technology might be more difficult to work with in the end). Finding Nemo-era technology would not really cut it these days. It makes sense that Pixar should put in a lot of effort to get this right.
On top of that, it's important to stay on the cutting edge, both in terms of keeping RenderMan a competitive product, and in terms of keeping the internal challenges interesting and fresh-- which is necessary for attracting top talent and preventing the company from getting into a rut or a routine.
