Cash is different: it is value based and accounts are not involved. A transfer of cash is final when the payer hands the cash over to the payee. The central bank does not register transfers of cash, only the initial issuance and the final return.
DBM held by non-banks could either be account-based – in this case, the central bank would open an account for every interested non-bank – or it would be value-based like cash. In this case, interested non-banks would need to be equipped with electronic wallets for holding and using DBM.