I realise it's not that simple - and I'm not a tech wiz at all, mind you! I just figure with everything else we know is being added (enemies, abilities, characters, animations etc.), everything that I'm sure will be added that we don't know about yet, and the fact that, looking at the trailers, landscape and design quality has not been sacrificed at all, I'd just rather bet that the map size increase that we will definitely get is more likely to be <99,9% than >99,9%, even if it's hefty.
Edit: I will be much more than happy to eat my hat on this, of course!