I don't think they can leapfrog traditional banking. If they can't access the banking, how can they buy or cash out bitcoin through the exchanges, which accept fiat money deposits for them to trade or transfer fiat money to your bank account for withdrawal?
Well that's where bitcoin comes in. They buy bitcoin with regular cash or get paid it for work or sent from their families via the remittance market. There will be independent businesses that will pop up like mpesa and others than will exchange coins for cash when needed.