The only way I could imagine any sort of "customization" like this would be in an extremely controlled form, i.e. a collection of five slots where you could choose either one talent or another. And then each choice would be constructed to make either choice better depending on the content, the group composition, or perhaps in some cases execution difficulty. And then make them change-able on the fly outside of duties.

For instance, if Bard had a talent slot where they could choose between a second Bloodletter charge and a second Empyreal Arrow charge, the former might be better in a full-uptime scenario while the latter might be better if there are a bunch of breaks in a fight, or if you're newer to the job. (not saying that exact assessment is accurate, it's just a hypothetical)

But they would have to be super isolated like that I think. Doing whole "trees" or similar would be way too difficult to balance in a way that legitimately leads to options. And even then, we still wouldn't really have options so much as a bunch of book-keeping to do before going into a piece of content.

SE is already pretty allergic to allowing player skill to matter, so I can't imagine they'd want to also add a knowledge gap where some players know how to arrange their traits for each fight and some don't.