i can't help but fee you are talking about something that already exists, similar to OpenBazaar. have you checked it out?
When compared to electronic means of payment:
Its transaction confirmations aren't instant, payment processing can be costly and custodian payment processing (holding) carries a market risk.
the only thing that you are correct about is the volatile price. the rest aren't true. all other means of payment have delays in their "confirmation" and they have costs even if you don't see them at first.