Looks like a proper add-on is on the way. Here is some blurb:
Source
I never know if it best to plough your 90 odd hours old levelled up character into these add-ons or start a new game.... still it sounds interesting.
First concrete details have emerged on Shivering Isles, Bethesda's first expansion pack for its RPG epic The Elder Scrolls IV: Oblivion.
Revealed in the latest edition of PC Zone magazine, word is that the expansion will offer 30-plus hours of new adventuring, features new quests, monsters, expanded freeform gameplay - quest lines that branch more than before, for example - and a new land "that you can watch change according to your vital life-or-death decisions".
Setting the scene, it's explained that an ominous-looking gate has opened in Nibben Bay, the portal leading to a torn realm - the Shivering Isles - ruled by Sheogorath, the god of madness and dementia. Apparently, adventurers will meet the god and "plough through his trials", but it's additionally hinted that ultimately we may well be usurping the deity. A ETA of Q2 2007 has been given.
Source
I never know if it best to plough your 90 odd hours old levelled up character into these add-ons or start a new game.... still it sounds interesting.