It's not a complete payment scheme by itself, as it's missing dispute resolution (a prerequirement for payments between strangers).
But who says that the same party has to offer payment rails and dispute protection? There are successful models of the two being decoupled in some markets (e.g. various providers offering fraud/chargeback insurance on top of SEPA Direct Debit in Europe).
Dispute resolution isn't required in most cases anyway. It's already a lot safer than cash, because a permanent record proves the payment did occur. Also, chargeback insurance, in expectation, does cost the user more than he saves.
None, which makes it a pretty suboptimal payment method for some transactions.
I'd never buy an airline ticket in cash, for example: If the airline were to go bankrupt (which has affected me more than once in my lifetime), I'd have no recourse.
But who says that the same party has to offer payment rails and dispute protection? There are successful models of the two being decoupled in some markets (e.g. various providers offering fraud/chargeback insurance on top of SEPA Direct Debit in Europe).