How about LinkNameIsPageName?
Text from multiple thread authors is on a single page
WikiNames are often phrases without widely agreed-upon meaning. Wiki participants cooperate to generate shared meaning.
FindPage seems like a WikiPrinciples feature to me. RecentChanges might also, but some features (e.g., no topic-based ability to look selectively at RecentChanges) seem more like WikiPrinciples to me.
RecentChanges is not necessarily a principle. It's just very common, but not universal. Moreover, RecentChanges doesn't scale, so eventually it will have to be replaced with something better. Some wikis (such as WikkiTikkiTavi, MediaWiki) have a system of subscribed changes; in the case of 'Tavi this is a functional superset of RecentChanges (as RecentChanges is merely one set of subscribed changes). Also, FindPage isn't a principle either because not every wiki has it.
Not every wiki has backlinks, but most still consider backlinks to be a core bit of wiki tech.
Q: Do we have a known set of wikis from which we are attempting to describe existing WikiPrinciples, or are we trying to understand some kind of unknowable wiki-ness which might lead us to evaluate some wikis as being "less wiki" than others?
A(1): We just have a programmerly-complex way of documenting our use of the word "Wiki" and other neologisms involving that word. Fortunately, a lack of time keeps the generation of neologisms to ExplainNeologism? from swamping the server.
Having just written a Wiki engine that is quite different from others I've seen (NoteWiki), I think AutomaticLinkGeneration has an additional principle that hasn't been mentioned: indicating which pages already exist and which don't. This has a huge benefit for knowing when you've hit an existing page, and when you've guessed wrong or misspelt your WikiWord. It also has the effect of spurring people to create new pages, though the use of the interrogating question mark.