iTunes has a nice feature called iTunes Pass ( https://support.apple.com/en-ie/HT203021 ). What it does is you create an entry in the wallet with your AppleID and it shows you the current balance as well as a 3D barcode. If you co to a Apple retail store (in the country where you have your account) you can show them the barcode and you are directly able to top up your credit.
Starbucks also add cards for the same purpose to your wallet.
So the idea for would be now that you add an entry in the wallet to show the credit left on the card. This would allow quick checks of the card balance.
The next generation of this feature then would be to add an barcode to the wallet. This barcode could include some sort of Unique User ID.
Now you add an feature to your app to support reading barcodes via the camera.
What would this be good for? Quicker way for money transfer!
Person A wants money from person B.
Person A flips up the wallet with the barcode. And person B opens Revolut, set the amount to transfer, scans the barcode. Done. Both get a notification of the transfer.
As the barcode is only be used to transfer the money to. It wouldn’t be bad if the barcode leaks.
To send the money, you still have to access the app (no decrease of security there).
This would addresses the feature requests of being able to see the balance easier and it would address the payment via barcode option that people ask here as several time.
Oh and bonus feature. Exporting the barcode as PNG. This would allow a street musician to print it and place it in the hat or guitar box.