PayPal, the eBay-owned global payments company, is reeling from the seemingly abrupt departure of its president, David Marcus, for a new job at Facebook.

When I interviewed Marcus in March, he seemed fully dedicated to his job, outlining a vision for how mobile payments would be money’s third phase, succeeding both cash and plastic. After joining PayPal three years ago through the acquisition of Zong, his mobile-payments startup, and shortly afterwards becoming its president, Marcus reshaped the company’s culture and streamlined its unwieldy array of products into the simple notion of buying things with your phone.

Why PayPal’s Ready For Ready

Along the way, though, PayPal, in Marcus’s words, “fell asleep at the wheel” when it came to developers. It failed to make its products simple and appealing enough for app creators to incorporate PayPal as a payment option. Into that void stepped a Chicago-based company, Braintree, led by entrepreneur Bill Ready, a veteran of two payments startups.

Braintree won customers like Airbnb, Uber, and HotelTonight, and bought Venmo, a startup whose person-to-person payment app competed with PayPal’s basic money-moving service. Unable to catch up, PayPal bought Braintree for $800 million—and brought Ready into the fold.

I sat down recently with Ready to discuss how Braintree was doing under PayPal. He laid out a compelling vision for how payments would be transformed by the inexorable rise of mobile.

On the desktop, he said, “everything is intent-driven.” In other words, we type something into a browser and get a response based on our input.

“On mobile, it will be context-driven,” Ready told me. He already has engineers building versions of Venmo for Google Glass and the Pebble smartwatch, anticipating a time when wearables will be mainstream devices.

It’s hard to imagine a better candidate to run PayPal. Ready has already shown he can lead a payments company focused on mobile products and developers. He now runs PayPal’s developer relations, which he’s combined with Braintree’s efforts. And he’s got an eye on what’s coming next.

And he’s already stepped into Marcus’s shoes on at least one job duty: He’s speaking in Marcus’s place at Southland, an upcoming tech conference in Nashville.

There’s also the obvious question: If not Ready, who could eBay hire to run PayPal? While Marcus assembled a talented crew around him, like product chief Hill Ferguson and VP of growth Stan Chudnovsky, none of his top executives besides Ready are obvious choices to succeed him. And if eBay passes over Ready, he might well leave—which would leave PayPal down even more executive talent.