I like ben_danger's idea to see the emperor in his office on Coruscant.

The one thing that has always bothered me is how short (at least on film) Luke's training is in SW5. I know there were several more training scenes planed but were ever filmed. I don't see how this could be adressed. I'm not saying it is necessary, but maybe an extra 30s to 1 min of some training related scenes would be nice. It would make Vader's line 'Obi Van has thaught you well' even better (Vader doesn't know Yoda has trained Luke).