But in the distant future it might look like this:
We can use some centralized "bitcoin banks" where ordinary people will keep their bitcoins.
If you are ordinary person you can keep some money in centralized "bitcoin banks" to use their fast network like Visa for fast small transactions. If you keep all money in that bank and that bank goes bankrupt, then it's only your fault.
If you have a lot of paper bitcoins and they are actually not backed by real BTC - it's only your fault.
How is this distant future?
We already have the banks with the vaults, Coinbase, Gemini, or smaller ones like Bitcoin Suisse, we have the standard banks that also offer trading and a visa card, with Binance and Crypto, we have the bankruptcy with MtGox or the total failure like Quadriga or MintPal or god how many examples of this type we have.
The distant future is already here.
Come to think of it, I'm actually part of the problem, I think I've used more my Binance and Wirex cards for buying stuff than real
BTC, I need to go in the garage and flog myself for 600 seconds.
Bank notes are IOU ("I owe you") papers. Central banks keep large quantities of gold to back that.
You want to give banks one more tool for printing more paper? What would make these Bitcoin-backed IOU banknotes better than the current fiat currency?
We could use real bitcoin banknotes, like the ones Tangem was developing, although I don't know how things are going with their project.
But, I don't see any point or real-life actual usage for any of those.