Well, they have had that in the UK for sometime now. The system there was already far more efficient than the US one when this was introduced - which is not surprising, it´s mainly a technology issue. The only thing it really changed was that deposit accounts received a slightly higher interest rate up to a certain limit, provided that you pay your salary into them.

So based on that, Account portability is not whatever it is that is stopping the US banks providing a service to the entire population.