Not necessarily a USB as an interface, and it shouldn’t contains any biometric either for privacy, just a paper replacement.

They are already RFID enabled (at least US ones have been for years).

You would want a paper version as a backup anyway in case the electronics fail.

The "paper version" is still required - the RFID is authenticated with information from the passport. The idea is at a border the passport itself will be scanned, OCR'd (from the data in the machine-readable zone) and then that information will be used to read the information + signature from the RFID chip to authenticate the document.

No, you're wrong. The person's passport number is a primary key into the issuer's database of valid documents as the ultimate source of truth. The RFID is another means in case the paper version wasn't legible, but at the expense of over-communicating details.