In practice there would be no good way to make it legally binding. Even defining what you mean by "selling out" would be incredibly difficult in plain English let alone codifying it in legalese.

I don't think you can trust an organization anymore than you can "trust" a weapon. A bad person could theoretically take control of it and use it for evil.

The closest you can get is trusting the individual at the helm. You know Automattic isn't going to do anything weird as long as Matt Mullenweg is the dictator.