I'd say that people taking it for granted that this was the last arc to the point of treating it as an unbreakable assumption, was their own fault. And it became really annoying at that time, people were filling the Pale threads with discussion of the "next" serial instead, and justifying it to themselves and others because Pale was supposedly effectively finished.
And I gather (though i wasn't around the reddit at the time, i think) that it's the same annoying crap people pulled with Twig, crapping on it as it was ending to talk about how stoked they were about Worm 2.
I don't want to ever hear people saying about how something is near the end unless they have absoluteky clear WOG on the matter. And even if something is actually ending, it's shitty to use its discussion threads to talk about the next thing instead.