To wit, the payments company released a study this week that revealed that 83% of people polled in five countries, including the U.S., wished they didn’t have to tote their wallets around, and if made to choose, 29% of Americans said they would choose their smartphone over their wallet if they could bring one item when going out. Unsurprisingly, those findings align nicely with PayPal’s (EBAY) strategy, which includes the expansion of its payments services in physical retail stores. By the end of the year, Marcus estimates PayPal can be used as a form of payment in 2 million U.S. locations. (This figure excludes the 7 million domestic stores that will be able to accept a PayPal payment card this year as part of an agreement with Discover (DFS).)

Given the rate of expansion, Marcus predicts many Americans — or at least a fraction of PayPal’s 110 million-plus active users — will be able to go wallet-less within the next 18-24 months. “There are roughly 9 million places in the U.S. that accept credit cards, but there are really 5 million that matter,” he pointed out to Fortune this week. And by the end of 2013, PayPal will be supported in just under half of that. “Then there’s another half that we need to get to basically be at every place you want to be.”

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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.”