Alas, I fear the whole issue of "story" is even more complicated by considering not just what "canon" is but what it will be. RAWA has said many times (or at least once, back at Mysterium 2003) that the D'ni story/universe is like a giant checkerboard, only a few squares of which have been revealed. Let's assume that Cyan has a massive D'ni History book hidden away somewhere, dating back to the beginning and going through the distant future. "Conflict with canon" could be interpreted as anything that conflicts with that history book, even though only a dozen or so pages have been read by we poor explorers. This is a problem faced by an explorer "D'ni survivor" storyline, for example. An explorer-generated D'ni survivor would have knowledge of D'ni, of course. His or her presence in the cavern would generate billions of questions about D'ni. Would this storyline automatically conflict with canon? No, not if the D'ni survivor's responses were limited to revealed canon. But what about a question about D'ni clothing? Or D'ni food? Or outdoor D'ni rock concerts? Either the survivor would have to feign incredibly selective amnesia, or else the survivor's answers would be taken as canon, yet possibly conflict with Cyan's notions of D'ni food and clothing and rock concerts.
Now, I agree with Blade's notion that everything that is done in-character in-cavern is canon, but there is canon and then there is canon. Creating story in a shared reality means that the creation of canon is incredibly flexible, and other players have to be light on their feet to accommodate the infilling of reality by other players' choices. This makes it hard to execute long story arcs without some sort of central direction or at least some screening. It also means that all players have to accept others as their equals in creating story, otherwise you could get "Story Wars," as players create canonical conflicts. In MORE, we won't all be equals, however. There will be the explorers, and then there will be Cyan - not an active player in the beginning, but still the keeper of that massive history book. I doubt (and actually don't want) Cyan will give us that book, although maybe they'll let us peak at a page or two. And so there will always be the problem of judging canonical conflicts not just in terms of the past but in terms of the future - where might Cyan go with their story telling, and how can any explorer group be sure that explorer-generated story won't conflict with or even foreclose some of those future paths?