Software productivity after all is about making the job simple for programmers. For one, the data exchanged between software components should be human-readable, machine readable, and automatically generated and consumed.
XML once was supposed to take that role. Unfortunately XML is overly complicated for human. Nowadays, it is JSON.
At the very bottom of software development productivity, it is the automation and structure of the software. JSON may play a big role there due to its simplicity and wide adoption.