Hey) I was also thinking of doing something like this - but more like Rogue-theX said keeping most of the original star wars and inserting scenes from Empire and Jedi - but would love to see other people try this!

one scene i had in mind: When the falcon emerges from hyperspace to find alderaan has been destroyed, the asteroid field is practically none-existant - so i was going to use the exterior shots of the asteroid field in empire to replace the exterior shots of the ships.

although theres only the lone tie-fighter in the original star wars, id try and work out a way to involve all the ships from Empire of that scene cos its just so great to watch.

I wasn't so worried about keeping the Skywalker story intact - it would have been just like an expanded version of the original star wars film.

When our heroes resue leia from the death star - its Hoth they go to, then you get to keep that stuff and then when they leave hoth they meet up in space for the briefing from Mon Mothma et al and then go to attack the death star. There would be some tinkering to do to get it flow smoothly.

The main problem i can't resolve tho is with the 2 death stars, especially the part where Leia is rescued from the first death star - but i guess for the final battle as most of the action would be of the rebel assault from return of the jedi - you could add close up footage from of the x-wings and Y-wings from the original movie...

hmm... a lot of tinkering tho and maybe some rotoscoping would be needed to make it convincing.

Feel free to use any of those ideas if you want, id love to see someone tackle this :)