Game worlds will only be as big as developers want them to be. Gen 6 we had games like Morrowind, True Crime Streets of LA, GTA San Andreas, Driv3r, Wild ARMs 3, Test Drive Unlimited, etc. Gen 7 we've had The Saboteur, Just Cause 2, GTA5, Oblivion, Skyrim, Test Drive Unlimited 1 and 2, Infamous, etc.
With gen 8, no idea how big the worlds are going to be yet, but we've got games like Destiny, The Club, and The Division which are trying to push the open world experience. None of these games may be as big as Just Cause 2 or Test Drive Unlimited 2 which are some massive worlds, but I don't expect them to be small.







