The MediaWiki Principles page (https://www.mediawiki.org/wiki/Principles) acknowledges that it is a work in progress. I think there is a very clear principle missing from it.
Wikis are an inherently populist mechanism. The original wiki, Wikipedia, was defined by it's taking of content once reserved for "experts" (encyclopedia publishers) and "democratizing it". Everything about wikis, by their nature, is about increasing access to knowledge.
Furthermore, if you read any documentation about Wikipedia, or wikis in general, the language used is always "we", "all", "everyone", etc. There is a very clear communal and inclusive nature to wikis.
As such, I believe that the MediaWiki Principles page should include, as one of its principles, the following (or some version of it):
...*existing principles* ...