Maybe that Modular and extensible should be a guarantee to those involved in adopting FFF and/or actively helping FFF to evolve. They both are then process-related, where one party might propose to e.g. define a ‘Licensing’ component to the specs, consent is sought, and they can start. And another party can request an existing definition of a concept to be extended with their property, which would go through an approval process.
Mentioning this explicitly helps parties feel more at ease, that they are not submitted to a specification where they cannot participate in the evolution.