As TESV: Skyrim starts, the High King of Skyrim has been murdered. Many wish to recede from the crumbling empire.
As TESIV: Oblivion starts, theEmperor of Cyrodill has been murdered. Many wish to recede from the crumbling empire.
I have no idea if you're just pointing out the similarities, or claiming the plot is rehashed and unoriginal.
Then again, it does stink of rehash a bit. Replace "Emperor" with "King", "Oblivion Gates" with "Dragons", and "Mehrunes Dagon" with "Alduin/Akatosh" and you get the picture. Oh, and take the "prisoner finds out he's an important figure reincarnate" from Morrowind and plop it in there.
Though with how the plot is, it does sound like it will be interesting because of the chance of another Dragon Break happening.
EDIT: Then again, we already did cause one of those in Daggerfall...