Bingowings said:

Everyone assumes it will be about the children and grandchildren of the Rebel heroes of the OT facing some old style new threat.

There is at least some mystery there if you ignore the EU (which I hope they do) but it would be more fun to have it about the children/grandchildren of someone killed by the Rebels of the OT.

Have them the new heroes and our heroes the new villains (well some of them).

Shake the thing up a bit.

Interestingly enough, I was reading some articles on that Secret History of Star Wars site the other day, and this lines up surprisingly well with what Lucas was talking about back in the 70's and 80's. For a while there he apparently had the idea that the prequel trilogy would be more political in nature (kind of like Dune I think, although none of the quotes mentioned it directly), the original trilogy would be light hearted action, and the sequel trilogy would be more philosophical, asking if good and evil were really as black and white as we'd seen in the other six movies. If they went with what you're talking about, we would have nine movies that actually matched that version of the "original vision."

Edit: Also with the whole Sith thing, Timothy Zahn mentions something kind of cool in the annotated version of Heir to the Empire, which is that when he was writing the book, nobody aside from Lucas himself actually knew what a Sith was -- for all anyone knew, it could be a species or a group that Vader ruled over in his spare time. He actually wanted the Noghri to be called the Sith, and he described them to look kind of like Vader's armor, and imply that it was based on them, but Lucas nixed the name. It's also why older EU novels were so big on the phrase "dark Jedi." The writers weren't entirely sure what a Sith was, so they went with something a bit more simple and descriptive, starting with Zahn.