The international nature of the Visa/MC/Amex/etc networks and the sheer number of banks involved makes me think this would be very difficult to pull off - doable, but not . Portable savings account numbers within Australia only would be easier IMHO as the relevant payment networks are basically run entirely within Australia, but even that would require major changes to banking systems.
If we're going to replace all the systems involved in card issuing anyway - what's far more interesting to me is evolving the payment system away from the current situation where we use a single set of numbers, printed on a plastic card, shared with hundreds or thousands of different merchants with varying degrees of security risks, as sufficient proof of identity to raid your entire bank account or line of credit. We have modern cryptography now, and if we used it properly, we could make Card Not Present fraud far more difficult than it currently is...