I've thought of something like this, though my version is a little more conservative, preserving Empire as much as possible. Some ideas to mull over, if you're interested.
If you're trying to keep it shorter than three hours, the final version would have to be mercilessly cut back.
- Open with A New Hope and continue as normal until Death Star sequences
- Use establishing shots and footage from Return of the Jedi to make it appear that the Death Star is still under construction (backed up by Imperial conversations about the station "not yet being operational", also makes the Rebels seem very speedy in their resistance)
- After the escape from the Death Star, remove TIE Fighter sequence, have the Falcon blast into hyperspace immediately after escape (mostly for time constraints, if all footage was included, the film would be over five hours). Leia reveals that the ship is being tracked.
- Shots of the Falcon flying toward Hoth.
- Cut to establishing sequence of Vader's fleet from Empire Strikes Back. Cut to inside Vader's chamber. Edit the screen so that Tarkin appears to Vader on it and asks him "if the homing beacon is secure", have Vader respond that he is "sure the rebels are in the Hoth system".
- Cut to an establishing shot of the Rebel base. Show R2 being hooked up to a computer console and having the DS plans appear on a small screen. After this, cut to Han entering Rebel command room and informing the general that he cannot stay and must pay Jabba the Hutt. Edit conversation so that Han retains some of his irreverent tone and so that the general shows less respect for him.
- Cut to Star Destroyer releasing probe droid (not so much searching for the Rebels as scouting out the base, so the Empire can launch an effective attack). After droid emerges from the snow, cut back to Rebel command as they track it. After Han volunteers to investigate, cut to Luke on Tauntaun traveling toward impact site - suggesting that Luke also volunteered, though of course there's not enough footage to make this transition completely smooth.
- After Wampa attack, cut to Han destroying the probe droid and the Rebels concluding that the Empire knows where they are.
- Cut to Wampa cave. As Luke hears the beast approaching he fumbles at his ice encased feet before hearing Obi-Wan's voice telling him to "use the Force, Luke" as in A New Hope. Luke eventually "lets go" and summons the lightsaber to him, escaping into the snowy wastes.
- Cut back to Rebel base. Han returns and begins working on the Falcon before 3PO approaches to reveal that Luke is missing. Han gets on Tauntaun and returns to the snow.
- Continue as normal - Yoda, Falcon escape, Cloud city etc. If any footage is to be removed for time reasons, it should be from Jedi. Remove mention of "another".
- After Luke discovers that Vader is his father, Han is encased in carbonite and Luke is given his new arm, cut to Vader arriving on the now complete DS to inform them that the Emperor will be arriving soon.
- Cut to Luke returning to Dagobah ("I have a promise to keep", etc.) to speak with Yoda. Remove mention of Leia as Luke's sister. After Yoda's death, cut to Chewbacca being delivered to Jabba. Edit footage so that this scene, not 3PO and R2's arrival, includes the dramatic musical sting as Han in carbonite is revealed. Maintain the overly suggestive reveal of Lando in disguise, as these are, after all, the two characters we saw head off to free Han only minutes before.
- The restructuring of the next few sequences will be difficult, but remove as much excess as possible (possibly Rancor sequence, dance sequences in general). Get to Sarlaac as quickly as possible.
- After escape form Tatooine, cut to Emperor's arrival on DS. Cut from Emperor's arrival to Rebel fleet establishing. Rebels discuss their plan, in an abbreviated fashion (possibly with less grinning from all involved, so that the mood matches that of Empire and ANH a little more closely) and then head off to Endor. DS hologram would have to be altered to depict a complete DS.
- Remove all superfluous conversations between Vader and the Emperor. Maintain mystery around Emperor by not showing his face until Luke's arrival.
- Cut down Endor considerably. Speederbike sequence either removed or cut down as much as possible. Cut excessive Ewok cuteness, speed through all Ewok sequences as quickly as possible by removing all but the most pertinent details.
- Luke gives himself up to Vader. Cut to Han and Leia at bunker. Rotoscope all but one Stormtrooper out. Edit Han's dialogue, "Not bad, there's only one of 'em", "It only takes one to sound the alarm", "Then we'll do it real quietly". Cut to Han and Rebels capturing lone trooper. Ewok theft of speederbike removed by these means.
- Cut to Luke's meeting with Emperor. Ground battle on Endor cut back to near non-existence. As the Emperor tells the commander to fire when ready, cut to Tarkin giving the DS operatives the nod. In the midst of battle, feature the brief scene of Tarkin being offered and refusing an escape ship. After DS is destroyed, cut to Han and Leia sharing an edited version of their kiss. Then cut to Luke burning Vader's body. Pan up from body. As we pan up into the starfield, credits begin to role over a more gentle, less triumphant Star Wars theme such as the Force or a selected piece from the PT.
Again, this version would have to be put together first and then subjected to a merciless editing operation to make it work, though I truly would like to preserve Empire as the beating heart of the edit.