Okay, I had an idea this morning. Let's say Zenimax released Elder Scrolls VI based on the following concept - would you play it?
In current ES lore, Daedra can be summoned to Mundus from their various planes in either their natural form (very briefly) or bound to something more permanently. They come in lots of flavors and the most powerful are the Daedric princes who control entire planes/realms.
So what if, rather than choosing a race of Tamriel (or any part of Nirn, for that matter), you must play as the Daedroth of your choosing, and you get summoned to Mundus for various reasons from time to time. These equate to the quests of a normal ES game. While in your home plane you can explore, work on skills and collect items/gear but when summoned you are stuck with what you have until you've completed the objective.
The open-world aspect would apply to your home plane, as well as Tamriel if there was a main quest line that would allow you to find some way to get yourself into Mundus more permanently, at your own discretion (like some Daedra are always trying to do).
Basically, the idea is to shake up player expectations and let you see the world of Elder Scrolls from the other side. Good? Bad? Stupid? WHAT SAY YOU!?!?