Banks will not even be forced to change anything regarding their current entrance on their internet banking software. If central banks talk about electronic money or blockchain, they do not think of bitcoin but something focused. They wanted to eliminate it in the year because everyone's financial track was their favorite. Then there is a monetary market "regulated" electronic money (electronic money is not new) and what we have with bitcoin and other decentralized currencies remains.

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Adoption of what? This won't influence the adoption of bitcoin.
If it's about the adoption of the new national cryptocurrency, Average Joe's won't care about the kind of the payment system at the bank. (if it's a blockchain based one or not). Banks even won't be forced to change anything in connection with their current frontend of their internet bank software.
The reason is simple, the digital national currency is just a different kind of digital form of the fiat that the central bank issues.
 If central banks talk about cryptocurrency or blockchain, they don't think about bitcoin but something centralized.

Bank of England is known as the central bank of the United Kingdom. The foundation of the modern central banks has been developed at the center. It is the world's second oldest central bank and the 8th Old Bank in the world after Sweden's Switzerland's Ritzbank. On July 17, 1694, a £ 1.2 million pound-sterling capital was established in the City of London as a personal financial institution through royal charter. Later, nationalization was done in 1946. [1] [2] In 1998, for the first time got autonomy from the government. [3] Yet it is controlled by the government. The Bank of England, established as a bank of the British Government, is the banker of the UK government. Mark Karen has been the Governor of the Bank since July 1, 2013. On June 30, 2013, he became the first non-Briton to replace Governor Marvin Kane for five years.

The Bank of England is the central bank of the United Kingdom and the model on which most modern central banks have been based. Established in 1694 to act as the English Government's banker, and still one of the bankers for the Government of the United Kingdom, it is the world's eighth-oldest bank. It was privately owned by stockholders from its foundation in 1694 until it was nationalised in 1946.[2][3]

I think this option is a good thing for their customers, but I'm not sure I would let Bitcoins deal with them. Those who are thinking that they will borrow easily with the BTC-USD return for trading purposes, this idea is not worth the price. But honestly I do not like the idea of returning fiat, in either case if the price goes up or down the only beneficiary would be the bitbank.

I don't see it practical as for some of the time period the borrowed Bitcoin will be locked so can't do any activity with it, at least not trade. Those who are thinking that they will borrow on easy terms of BTC-USD pay back for trading purpose, this idea don't worth them. For some of the people like escrow it may work.
But honestly speaking I don't like the idea of paying back into fiat, in both the cases if price goes up or down the only beneficiary will be bitbank.