Here's an interesting nugget from the Elder Scrolls forums, posted last week. Bethesda employee mburg responded to the most recent thread discussing Oblivion expansion packs: "We have no plans to make an expansion for Oblivion. Should that change, we'll make an announcement on Elder Scrolls.com."
The steady stream of downloadable content Bethesda has been providing only adds incremental enhancements to the best selling RPG. However, you can still get lost in Tamriel for months. So do we even need an official expansion, or are mod communities such as The Dark Brotherhood Sanctuary enough to extend the Oblivion experience for years?