I'm thinking that Lucas will probably be avoiding live action from here on out. He has had way way way too much success with the Clone Wars animated series. He can actually tell the stories he wants and show the wild exotic things he dreams up without all those messy actors, special effects or overwelming costs getting in the way.
As far as Jacen and Jaina? If he were to do anything with them I can't see it being anything much later than the "Young Jedi" early teen period. Which would pretty much wipe out or invalidate any of the later books. Something set not too long past the original Zahn books. And even then it would be a strategically poor topic to film.
Now I think after Clone Wars ends there is a huge chance we will see a semi continuation of it...
And really a friend just talked me into watching the Clone Wars series. I gotta say it is George's best work since Empire. A total reversal from all that was the prequels. He seems to have learned from the prequels. While he puts forth and gives final approval to all stories but he lets others actually execute the show. And wow what a difference it makes. If you can make it past the pilot movie and the big headed animation style you will find some great Star Wars stuff in there.
I have one issue with the clone wars series. If you look at my sig, you can tell why. I mean, first you destroy the cannon of the Republic Commandos series which gave a compelling glimpse into the world of soldiers of a slave army as well as the best descriptions of Mandalorian culture! Karen Travis even translated parts of the freaking language Mando'a
. Other than that I don't mind the animated series that much.
As for a movie for the twins... I'd say not. To much back story to fill in for people who missed the old stuff. I'd love to see it but it probably won't happen, sorry.