> from a pure technical point, double-entry bookkeeping is no longer needed at all

Just because databases are transactional doesn't mean the entire system is. Double-entry accounting still helps catch errors.

A concrete example, since people like to think databases dealing with money are especially transactional, when they're not ...

I used to work at a small regional bank. In the course of some network maintenance, I accidentally disrupted the connectivity to an ATM while a customer was doing a transaction.

The next day, our accounting folks caught a problem with reconciliation, and the customer called to follow up as well. My interruption caused a deposit to proceed far enough to take their checks and money, but failed to credit the customer's account.

It's very hard to orchestrate transactions perfectly across multiple organizations and systems. You can't hand-wave this away by pointing at db consistency guarantees. Traditional accounting techniques will catch these errors.

I'm not sure that ATMs even have the ability to communicate certain failure classes back to the acquiring bank. eg, a cash dispenser malfunction is common enough to be mentioned by VISAs network rules explicitly, but as far as I know will almost always require manual reconciliation between the ATM operator and the network.