Edit: Been told that it is a mordor army. Which means it will be an osgiliath type battle. WIth the new osgiliath terrain that makes sense.
This box is also rumored to contain new wargs, which are bigger than the current ones, whether they have riders or not has yet to be determined. Maybe wild (i.e. misty mountains) wargs are smaller than mordor/isenguard bred wargs?
Take it all with a grain of salt as this is pretty slim information.
And to you I say "Good day sir!"