My understanding has been that Zcash’s intent is to be like digital cash, meaning to restore individual financial privacy and autonomy that was lost with the arrival of mass surveillance by providing a way to financially transact that aspires to be as private as physical cash transactions. An extension of that could be to protect financial privacy and autonomy from further erosion as a consequence of developments in AI.
Zcash hasn’t yet reached those goals in my opinion, it still falls short of the maximum privacy and security that may be available when transacting with physical cash. Proof-of-Stake fixes part of that, it significantly improves Zcash’s security, and there has been constant, intense, and ongoing effort in further improving Zcash’s privacy, which I believe is already the best available of any blockchain.
I think the most meaningful definition of “cash” in the context that Zcash is concerned with is “liquid assets including bank deposits and marketable securities”, and that’s why there has been so much interest for so long in deploying Zcash Shielded Assets.