Future expansions.

And their emblem features the Sun, symbolizing Elrath, the Dragon of Light...

But not the dragon itself. I think the Tribes of the East will have an emblem in the shape of a crystal. IMHO.

Well, I understand it's hard to imagine. But there's another point: will they really not include it just because of its size? That would be quite disappointing; there should be more serious reasons for such a decision.

They are obsessed with dragons as representatives of the elements (earth, fire, darkness, etc.). They will claim that Heroes 6 is Might & Magic: Heroes 6, not Heroes of Might and Magic 6. And they will also say that we already have enough of a dark dragon, or that this is just a black dragon with a different name.