That would have to make it one of the longest game series in history. Let's see... 9 provinces x 4-5 years each = roughly 36-45 years plus it would probably take at LEAST 5 years to make the final one, so like... minimum 50 years. That'd be difficult to achieve.
Well, when Skyrim is launched, they have already covered High Rock, Morrowind, Cyrodiil and Skyrim. (Not including "spinoff"-games)
That leaves Elweyr, Black Marsh, Valenwood, Sumurset Isle and Hammerfell(not counting the part included in Daggerfall) = 5 provinces to be covered. 20-25 years after Skyrim, then.