Banks love blockchain techonology for a while already. They just hate bitcoin and make everyone hate it so
they will have someone uses their digital currency developed by them If so, banks will clone blockchain and clone bitcoin and use that coin for transactions. They wont ever use bitcoin.
Banks hate bitcoin.
Any kind of commercial banks (as are the banks you have in mind) cannot do/stamp/create its currency. Cannot do this because is not allowed by low. Only the Central Banks of a country have such right. So your "fear" about various coins, which can "compete" with bitcoin, created by various commercial banks is not at all possible. This is the first thing. The second one is that even this could be possible (cannot be) any commercial bank have not any kind of interests to do so. They don't (can't) own any kind of currency and have no interest to do (to ask permit to have) one such. If yes then every such bank will have its own currency and the finance world will be drown with hundred and thousand coins which will have value (probably) only for the commercial bank which have issued/created that and other few with which this commercial bank have connections. And if will be known by other commercial banks have no meaning to exist such situations. Full of fees for conversions or/and of transactions between those. Who will use such kind of service? Where will be the profit for every commercial bank for this kind of activity?
You are right, but there really seems a possibility of some countries to try this out as they have blockchain already as a gift which they can use to draw their one-end transactions easily towards the other end...
But, this really ain't a threat to Bitcoins, as Bitcoin itself is a completely new, innovative and different technology and even if they start up with a new virtual currency, even they will have to wait at least half the years Bitcoin took, to get developed; that too, not completely...