Maybe if The Witcher 3 got a close success like Skyrim (Oblivion if was even a great game, do not got the success like Skyrim, maybe Witcher 2 will be the Oblivion of CD Red) they will enough buyers to make expansion to sell and get good incomes, maybe even if The Witcher 3 do not take all the places that every reader of the books love, they will came on a future with a Big expansion that include, big territories and new endings
One example of a good expansion is the expansion of Dragon Age 1: Awakening
A bad example is a DLC from CoD (like map pack) or Suits from Saint the Row 4
A good example of a DLC is "Tiny Tina's Assault on Dragon Keep " which is a great DLC but still no like a expansion.