Well not only would it be impossible to have Vader vs. Palpatine, it would be pointless, as well. I mean, really, if they duelled, it would be over within a few seconds. Palpatine doesn't even need a lightsaber (I think ROTS needs plenty of work in this regard), he'd peel Vader apart with ease, just using the Force. As was said, he's the evil counterpart to Yoda, and Yoda would kick Luke and Vader's asses at the same time, without a lightsaber.

Now obviously Vader kills Palpatine, but that's only because he got the drop on him, and Palpatine still managed to get a fatal blow in.

On a different note, I know most people hate the Ewoks, and most reasons for that are obvious, but what sort of things can be done to make them a bit less childish? Obviously, removing their antics is key, and doing things like adding Stormtrooper helmets in their village as in the mockups, to make them seem more like strong warriors, are great, but it doesn't get past the fact that they are cuddly little teddy bears with spears. I assume Adywan will want to Cantinize their faces, but what about changing things like eyes completely? Or changing their voices to be more agressive and threatening? Just small things here and there in their appeances, since they inherently look childish, to try and minimize that.