They need bitcoin to use it reseve asset.
So if. China bank needs eur currency they dont need direct buying or exchanging china fiat to eur or find correspondent intermediary bank to do transactions.
They can do the transactions with btc or eth works too.
Btc can replace all wire and swift transfers between banks.
When jp morgan want to send funds to japan they just send btc their wallet.
And its a instant world transactions
See the thing is it is really not easy to make the banks accept cryptocurrencies like bitcoins. But undoubtedly they are the best options for the online transactions which are done beyond the borders. But the banks will try and then put their own commission on anything that they are going to provide as an option.
What banks can do is :
They can support the crypto transactions with the bank account without any interference.
They need to stop giving out statements about how they will close the accounts if they are connected with cryptocurrencies.
They should work with cryptocurrencies instead of thinking of them as a competition.
They can not only save bucks if they decide to do online transactions using bitcoins but they would also do it in a much less time.
They can actually set up btc accounts all over the world , send the money over btc and then the other person can encash and send it locally. (I do think it would work really well )