For those people interested in all things Oblivion who visit the Menori blog the official annoucement was last month by Bethesda. See the posting here. Make sure you search for isles with an ’s’ in it. I noticed some people finding menori.com by searching for ’shivering iles’. That would because of this comment which was posted a while back.
The expansion sounds very interesting with 30 hours of new gameplay in the realm of Sheogorath, Daedric Prince of Madness. If you’ve done the Daedric shrines quests from the original Oblivion content you’ll know that the reward for Sheogorath’s quest was the staff ‘Wabbajack‘. So if that quest is anything to go by this expansion is going to be bonkers. 