I don't have anything to back this up, but maybe that's why some of the plug-ins have been sub-par. I think that's where their attention is focused. It would be worth $20 to me to have a Hammerfell or Summerset Isle addon.

That's a very good idea. I agree. I've heard speculation that this is what Bethesda will do for expansions since Cyrodiil is so central to everything. I"m sure people will be making mods for the other provinces. Now that Blender will make modeling for Oblivion possible.
The Imperial style architecture we've been given for Cyrodiil isn't at all fitting for Black Marsh, or Valenwood or Summerset. Possibly might work in Hammerfell, High Rock and Skyrim. But actually each province has its own architecture just like hlaahu, redoran, telvanni, velothi were all unique in Morrowind.

Well I think after the release it was mentioned that Bethseda was split into 3, 1 part doing non elderscrolls stuff, another working or planning on the next elder scrolls and the last part working on oblivion stuff, whether that is just mods and patchs or includes expansions I don't know.

I don't think they will go to Hammerfall because of Daggerfall. A lot of people suggest Summerset Isles because apparently "there is all this talk about the Summerset Isles in game", but Summerset Isles is one of the least mentioned provinces, Valenwood, Elswyer and the Black Marsh get atleast twice as many mentions. I don't really care to speculate where they will or won't go next but Skyrim is a possibility, but so is everywhere else.

I don't think they are creating an expansion for a whole province, it would be ridiculous. The plug-ins are sub-par because they are sub-par

Wurlon makes a good point ... making an expansion for a whole very populated province would be just too hard to do it justice. But there are less populated or at least, less technically built up provinces .. so maybe Black Marsh or Valenwood could be a possibility for an expansion. Kind of similar to Solstheim which I know was just an island but it was very underpopulated. I liked the expansive feel of it.

Or they could do an expansion of just one city in another province to give us the feel of that province. I think picking central Cyrodiil was a smart move if they are going to connect any provinces by expansions in any way.