In my education, I've learned about a lot of languages whose case systems have atrophied, especially from PIE. Wikipedia had a reference to The Evolution of Case Systems for Marking Event Structure, but that was focused on language games (abstract below):
Case has fascinated linguists for centuries without however revealing its most important secrets. This paper offers operational explanations for case through language game experiments in which autonomous agents describe real-world events to each other. The experiments demonstrate (a) why a language may develop a case system, (b) how a population can self-organize a case system, and (c) why and how an existing case system may take on new functions in a language.
So, has any modern language added a case? I'm most curious if, for example, the grandparent generation lacks a case the current generation has.