Guild Wars 2 might never have an expansion, and that's a shame. The odd thing is, I can't really explain why it's a shame.
I can see the obvious downsides - the lack of another big launch, even less paid content, not "huge" world-wide changes - but all of these things are, I suppose, possible with the current Living World mode of updating. So why is there a problem?
Because expansions are the way things have always been added to games, and that isn't the case any more.