I've been reading this thread and I'm amazed at all the great ideas that are in it!

Anyhoo I've always wondered what Vader is thinking when the Emperor is engulfing Luke with the Force lightening, theres obviousley something going on in his mind and something that triggers his destiny to do away with Palpatine, soooo how about inserting some flashback dialogue ie

Queen Amidala: You're a slave?
Anakin: I'm a person and my name is Anakin

And at that point Vader turns on Palpatine.

Just an idea..