I feel like any synergy system would either have to be generic and watered down (for example, the example in the OP would be any invul skill+any regen skill or shield to similar result) or not possible without giving the more poisonous parts of the community more reasons to be toxic about.

There is a balance issue here. I think the devs' goal is to have every Job be viable in all content and thus skillchaining has a delicate balance that could serve to benefit a handful of jobs at the expense of some others. Plus it introduces a layer of complexity to existing jobs and comps.

It would be cool if it happens though,but I woudne't expect it outside of another XI throwback like Eureka