That might be the case, however, since this is not the Fallout universe, in which you play in one piece of land, with no telling from previous games of bordering regions, they might add a large chunk of land.
They might also add DLC which let's us go past the ocean water.
They've pretty much included all of Skyrim as far as I know, and the tradition of Elder Scrolls games means that any content will be restricted to the relevant province. The likely result of DLC will be more quests and locations on the existing map, and perhaps a new plane of Oblivion, i.e. Shivering Isles.
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