I am very excited about this cast. I am liking all of the actors on board here but I am especially pleasantly surprised to see Sydow and Serkis involved - both are amazing actors no matter their role.
For someone of his talent, I wouldn't be surprised if Serkis actually plays two charcters, one looking as himself and another as a motion-capture character. We'll see!
I wonder if there's no Billy Dee because JJ heard the rumor that Ady might kill him off in ROTJ:R ;) seriously though, I think its good not to have a complete reunion all at once, or at least a brief, surprise cameo will be fine.
I have to say I was really hopeful to see my favorite actor of all time manage to grab a role. Gary Oldman. That man is a chameleon and an amazing actor in all of the movies he's in. He would have been excellent in SW.. there's always 8 and 9 :)