...I think that the 'real campaign' is going to actually be a real campaign - a series of events in a conflict between the Kingdom and the Empire (Humans and Fallen respectively). I think the Master Quest victory condition will be something else entirely. I mean, they've even released an official map of the world, which I presume would be the world in which the campaign occurs. It'd really be false advertising to say "this game will have a campaign" and then you get into it and realize what they meant by campaign was really just a method of achieving victory in sandbox mode.
Not to mention it'd mean that the Master Quest would be the same every time for it to make for a decent, let alone good, campaign.
I wasn't being very clear. My speculation is based on GC2, which has a campaign composed of linked scenarios. Scenarios can do things like apply a saved map instead of a random map and require a specific victory condition. So I was imagining that the Elemental campaign is on that canon map and the only way to finish the campaign is to complete the Master Quest. Maybe. (Why is it so easy to assume someone is making a statement of certainty when all some of us are doing is thinking out loud and asking questions?)
On the "same every time" point, I don't see how that jibes with Brad explicitly ruling out scripted campaigns. Maybe we're having some (more) terminology confusion? Anyhow, like Scoutdog, I'm still hoping that the Master Quest is actually a set of quests unique for each faction. If 'the campaign' is driven by the Master Quest end-condition, that would make it effectively 12 campaigns, which sounds swell for replayability to me. (Not that I've ever tried to finish the GC2 campaigns--there's too little story in them for me and too many annoying scenario parameters.)