The Gamebryo engine has actually been used for turn-based games before (E.g. Civilization IV). It would just require a lot more time to implement than Obsidian has, and Bethesda probably wouldn't want it.
I had no idea. Civilization 4 doesn't seem to have much in common with TES series. Anyway, turn-based combat wouldn't work well with first-person(and third-person) viewpoint of Fallout 3, and an isometric view would take away much of the greatness of exploration. Like I said, we have V.A.T.S., and I'm sure character skill will have a strong role in New Vegas. It did in Fallout 3, to a degree. New Vegas will have V.A.T.S., right? Also, how would the isometric view work with the style of exploration Bethesda introduced to the series? I understand your dislike for player shooting skill, but there is plenty of room for character skill with real-time combat, and Vegas looks the best from Fallout 3's viewpoints. I'm excited to explore a well-lit, post-apocalyptic Vegas, and it just wouldn't be the same with an isometric view. I strongly support character skill, though.