Honestly the best use case is actually for the very financial services industry that the crypto community thinks they are supplanting. Distributed ledger with trusted confirmations + quicker and cheaper wires is actually pretty big. It's a rock solid use case that a couple of big banks have openly said they are working on. Of course, it's almost certain that any currency they move will probably end up pegged to a fiat, so that idea doesn't give people the warm and fuzzies, to say the least.