> And besides that, banks need capital reserves in the form of customer deposits

USA's fractional reserve requirement is now 0%. UK has also gotten rid of their reserve requirement as well. In the UK, the limit to what the bank can loan out is more determined by the market cap of the bank (committed shareholder value). Cash is only strictly needed to cover ... customer deposits.

So in the UK, if a bank gets rid of customer deposits entirely, then it kind of doesn't need any cash anymore. It can just lend money out of thin air based on its total net worth (market cap).