I've had the DVDs of the two Star Wars trilogies for a while, but never had the free time to watch them in story sequence until recently, while recovering from illness. The remastered original trilogy looks great, Lucas at last having the capacity to make it look as he originally conceived it. The dialogue is of course as clunky as ever, but the great sweep of the story still carries you along, first the tragedy of Anikin Skywalker, then the triumph of his son Luke in the face of the same moral dilemma and the eventual restoration of Anikin. Lucas is often said to have conceived the story as three trilogies. He now says that this is not the case and that the 6 films we now have are all there will be. Looking at the story arcs, it does look difficult to think of anything that would be anything other than a warming over of themes in the first two trilogies.
One interesting option would be to take the story a long way forward and marry it into the world of Ian M Banks' Culture novels. There are seeds in the two trilogies that could be picked up and developed, like androids and the various mechanical creatures that inhabit the background of many scenes. R2D2 and C3P0 might even survive into that future. A conflict between the straight laced Jedi and and Bank's Special Circumstances would have the potential for a great deal of moral ambiguity and allow the storyline to explore some of the less acceptable aspects of the Republic like its excessive centrality.