The big old card companies might look ripe for disruption, facilitating as they do high “interchange” fees levied on merchants (averaging 2% in the US). But thanks to the spread of their operations into every corner of the world, it has been either impossible or economically unappealing for potential competitors to build new kinds of networks. The big question, amid such a frenzy of fintech innovation, is will that change? There are several reasons to think it might.