Swapping out cards costs XP? That's lame. If a deluxe box or mythos pack comes out and it has cards that would be perfect for my current deck, I don't care if I'm mid-campaign, I will swap out cards for the new ones, XP be damned.
The deluxe boxes are supposed to be the start of the campaigns, so you wouldn't have to pay xp to swap cards at that point. (Unless you're still playing the previous campaign when you get the deluxe, I suppose.)