I think pulling off something like this would be very difficult for this simple reason: If Luke is successful and circumvents the creation of the Empire, then the OT loses its significance. If he inadvertently spends the PT trying to prevent the Empire, but somehow does things that cause it to be created anyway, then the PT loses its significance because its events didn't change anything. The latter, though, could be an interesting narrative on destiny or the nature of the Force, depending on how you wanted to spin it.

That was my big beef with X-Men: Days of Future Passed. The only purpose of the movie was to bring back characters that were killed off several movies ago. Likely, Fox realized "Hey, we can't have any new stories with these characters because they're supposed to be dead. Let's put Wolverine in a time travel story so we can undo the dumb choices we made in writing the previous movies." In other words, it was a big **** you to the fans and to all of the movies that followed X-Men 2. Not exactly the best way to manage your film franchise, IMHO.