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?
Swap it for M Pesa? There's already a parallel economy operating with that. BTC would run alongside it. There could be a huge volume of bitcoin exchange and cashing in and out without any of it ever touching a bank.
The question is whether it would be relevant to the average M Pesa user. Probably not that much in country, but there would be international applications.