Perhaps of note for engine worries, in the most recent Bethesda podcast, ( http://bethblog.com/ ), Todd Howard said that they "started designing the game after Oblivion". I don't know if that means anything for anyone on the board, (as I don't know how long it takes to build a new game engine), but I just thought it might be worthy of notice.
Not much in the podcast though other than that little tidbit and teasing that a lot of things will be revealed in the next months Game Informer.