Swedish banks already do this. They first implemnted their own systems with custom hardware (and before that banks mailed a physical scratch pad with codes) but

Swedish banks already do this. They first implemnted their own systems with custom hardware (and before that banks mailed a physical scratch pad with codes) but then later together developed a mobile app (called Mobile BankID) which can be used for authentication. So clearly it can be done. Swedish banks have been doing it for at least 20 years.