Besides going wallet-less, something else occupying Marcus's mind nowadays is digital currency, the most popular of which right now is Bitcoin. Currently, Bitcoin is an unregulated, online-only, synthetic currency created in 2009 by a programmer known only by the nom de guerre Satoshi Nakamoto. Controversy has followed Bitcoin in recent months thanks to volatile exchange rates—one Bitcoin was worth $20 this February and was worth $230 by early April—and concerns that the currency is being used for illegal activities.

In many ways, Bitcoin promises to fulfill some of the grander ambitions PayPal's original founders, including Peter Thiel, had for the service. Now, Marcus is closely following Bitcoin and the space. "It's very well designed, the way that specific currency is being designed," admits Marcus, who says it's more like stored value than an actual currency. "People think it's a potential alternative to dollars, but it's more an alternative to gold."

He's optimistic that within the next couple of years, governments could legislate Bitcoin—or which ever currency remains most popular—and if they do, he suggests PayPal support may not be far behind. Wonders Marcus: "The big question is whether it's going to go mainstream or stay limited to just a few zealots and criminals."