In the abstract, money is clumping
As a result, a system based on money is always going to have clumps, whether it’s brain drain that takes smart people from poor nations to lands of opportunity, or whether it’s clumping in time that leads to boom-and-bust cycles. It’s this inherent clumping nature that represents its main inefficiency.
The future of money is eCash everywhere, spreading money under a thousand mattresses, telling every cashier, "Here, try this card."
The unbanked will have eCash everywhere. They'll have cash on Facebook credits, on SnapCash, on PayPal, on unused MoneyPaks, and/or on gift cards. Paying for goods will be a matter of cycling through various balances. Security for them is in spreading themselves thin, having cash all over the place. If any one account gets compromised, it's as big of a deal as losing coins in the couch.
Bitcoin may provide the virtual glue between all these systems, though, so paying for a hot dog at the convenience store may use some obscure ePayNow-like service, with Bitcoin being used in the background.