I haven't looked into really. Its going to have the usual extras, and probably a few we don't expect. The main one is probably the explaination of the Prophecy of Anakin as the Chosen One and give a more definite answer to that.
I'm more interested in listening to the dvd commentary during the movie though during key scenes so George can explain those. I'm mostly looking forward to seeing how he explains the Sidious/Windu duel and the Sidious/Yoda duel. These two duels have a lot of controversy about them (such as did Sidious truely throw his duel with Windu because he knew Anakin was coming and he needed to look like the victim so Anakin would be forced to make a decision to save him, or did Windu legitimately beat Palpatine and the rest is true and Palpatine just took advantage of the new situation).
Palpatine fans, such as myself think of what happened in two different ways:
Palpatine set the entire event up, starting by revealing to Anakin who he really is knowing that Anakin, still loyal to the Jedi Order, would tell any available Master of this news.
Palpatine didn't necessarily know who would come to arrest him, but he knew some would, and that it would be more than one and some or all of them would be Masters.
This shows us that Palpatine clearly wants to eliminate as many high-ranking Jedi as possible before he executes Order 66. If more of them are dead before the order is executed, then theres less of a chance for the Jedi to fight back effectively (whichever ones survived order 66 and/or any that remained on the capitol and jedi temple.)
Palpatine knows that they know now he's the Sith Master, and he doesn't hesitate to use the Force immedietely after the arrest attempt in his office. He leaps over his desk and kills 3 of the Jedi Masters (all council members as well) in mere seconds and forces Mace Windu back. A favorted tactic among powerful Sith is to save the strongest opponent for last.
Most people, regardless of what their opinions are, will not disagree with what's happened thus far.
Now, this is where there are two opinions in the Chancellor Palpatine/Darth Sidious fan group:
1.) The duel itself. Palpatine was superior to Windu and was simply toying with him, buying time for Anakin to get there because he's already tempted him to show up. He parrys with Windu rather than going for a kill for this reason. He puts himself in a life-threatening situation with the Jedi Master by allowing himself to be disarmed at the right time in the duel but knows that Windu will still try to arrest him (Windu even still wants to at this point) "You are under arrest, my lord!" He (Palpatine) needs Anakin to be there to make a choice and he's confident Anakin will side with him when it comes to Palpatine dying (Palaptine can't be allowed to die because Anakin believes that Sidious can save Padme).
or
2.) They are equal or Sidious is superior, but his form of saber fighting versus what Mace uses keeps Palpatine from putting an end to the fight (if he wanted to, but he didn't so this theory doesn't need to be tested). The duel is balanced much like the Yoda/Sidious duel therefore, and neither man gain an edge over the other or can at this point. Sidious doesn't even need an edge over Mace, because he knows what will happen anyway. Its not until Mace Windu delivers the spinning back kick to the face that causes Palpatine to lose his saber and be backed into the corner. Sidious forfeits the duel in order to win the prize- Anakin Skywalker.
The Mace Windu fans believe it a different way for the following reasons:
Palpatine could not have possibly forseen that Anakin would show up at the necessary time or that any of these precise events could have been planned. He's simply not that powerful in the Force. Therefore the entire confrontation with the Jedi, while intentional, was not predictable in his eyes, and while able to kill three masters, he could not kill Windu without Anakin's help so long as Windu had his lightsaber (though many will admit that Palpatine's lightning was so powerful that Windu couldn't hold him for much longer at that his saber would fail him).
As a Palpatine fan it will be a blow for sure if Lucas says that Windu legitimately defeated Sidious because either he's the better swordsman or he merely beat him this time (in other words, if they faught more than once, then hypothetically the result may not be the same).
I think its clear through that the Force was stronger at this point toward Palpatine and his usage of it, which fuelled Palpatine, while in the future, the Force aided Luke.