Thought experiment:

- Be a completely regulated Ecash custodian

- KYC your customers as hard as you can

- Make them authenticate for every ecash transaction

- Log everything in your database

- Know how many users you have, and what their balance is

With all this, you can still have:

- Instant payments with zero fees

- Offline payments (no internet required for payer)

- Anonymous payers, authenticated receivers

- Programmable ecash (spending conditions)