I don't think bitcoin-bills would be that feasible to use. It would be hard to give a change using those bank notes. Besides, wouldn't it be better for us to improve the current bitcoin we have today? I mean we can make paying using crypto easier via wallets generating qr codes and the likes when one clicks receive. The qr codes will execute automatic commands to send a certain amount of btc to a certain wallet every time we scan one(it would be possible to do in the future). I think it would be good when paired to a fast confirmation time.