In that chain of events, throw in Justin Bruening as Jacen Solo. I know he's a bit old but I think he could pull it off - I've enjoyed watching him in Switched at Birth.

Perhaps, in a non-EU timeline, the ST could focus on Luke training Jacen. Go with the familiar turn to the dark side theme, with Ep 7 combining the best elements of Eps 1 and 4 to establish the relationships. In Episode 8, build up controversy between Jacen and Luke, show Jacen leaning towards the dark side, argumentative, etc. and have him give up on being a Jedi and disappear at the end of the film. In Episode 9, Luke tracks Jacen across the Galaxy. At the end of the film, there can be a light saber battle between Jacen and Luke, where Jacen obviously has the upper hand. He begins to toy with Luke, and eventually goes for the killing blow, stopping at the last second with a change of heart, then helping drag Luke to safety (insert cliche self destruct sequence with timer).

This combines Anakin's fall to the dark side with Luke's self-redemption by not killing Vader in RotJ. Keeps the story in line with the rest of the Saga, ultimately tying up the whole thing and showing that someone truly could be completely redeemed of the Dark Side. Sure, Anakin was at the end, but you never got to see him do anything good in a post-Vader life. Of course, you'd need another driving plot device (Yuuzhan Vong invasion perhaps) in the background.