There wasn't much foresight required on his part because companies were already doing things like this way back when. As a trivial example, patents on DRM predate the oft-cited "Right To Read" by a decade or more. Stallman just observed these trends and took an opposing stance without (to GP's point) really addressing the economic incentives and nuances involved.

Maybe his biggest contribution is that his extreme stance and ensuing visibility probably helped shift the Overton window.