They could do something like "Elswyr" or "Black Marsh", a game using the Skyrim Engine, but built in the vein of New Vegas, so it had the obsidian touch.
I personally could see why Bethesda would be hesitant to do this, however, I think it would richen the brand - heck they are doing ESO, why can't they do another Obsidian Spinoff like they did with New Vegas?