Well firstly they called it the "First Graphical Update" which implies a second is expected.

Secondly, they have mentioned about how, I think it was the bones, were developed with future-proofing in mind so that animations could be improved retroactively in the future.

Thirdly, they have changed running animations before a long time ago in a patch. They gave each job a unique sprint animation which did not used to be a thing, so they could do more things like that someday.

Although I don't know about Ray Tracing, I know that lighting is a massive part of the design process and they put a lot of attention into it because, for example, it had a massive impact on how Amh Araeng appeared (this was one of the examples they showed in a development panel discussing the lighting). They also put a huge amount of work into the sky and the weather. In other words, if they switched to some more automated method, it could affect or ruin the work they put in to making zones look a certain way. That is most likely why they haven't rushed to do it.

Obviously they will be likely to drop PS4 when the amount of people using it is low enough, although I think many FFXIV players would just upgrade anyway if pressured to.

The engine is capable of a lot more as you see in FF16, but they limit it on purpose for various reasons. Some of those reasons might make sense (like the effect on a PS4 player or the effect in a congested area) but other times it is due to infrastructure decisions or a mindset thing.