Although a 3-in-1 edit would have been neat, it’s probably unfeasible as you say. But a 2-in-1 ESB and ROTJ could be really good, and I had actually been thinking along those lines for a theoretical fanedit.
Open with Palpatine’s arrival at the partially destroyed Death Star. He senses Vader wants to continue his search for Skywalker, and says that Luke will eventually seek him out.
Cut to Hoth, and Luke’s misadventures in the snow. He is knocked out by the Wampa and remains offscreen while the Probe Droid plot is moving forward.
The Emperor dismisses Vader to go wait on the command ship, where he hears his officers talking of a transmission of the Probe Droid. Vader’s decision to follow it despite his master’s insistence that he have patience is now a foreshadowing of their familial connection and weakness.
The Imperial fleet arrives over Hoth as Han is still missing, looking for Luke, and then a search party is sent out and find Han even as the walkers advance on the base to drive up tension. Cut the Bacta sequence and skip straight to Luke suiting up and getting in a speeder.
The asteroid chase could again be cut in favor of simply putting the Falcon on the Star Destroyer.
Luke’s training could be shortened, Vader’s communication with the Emperor can be cut because of redundancy.
Lando and Leia escape Cloud city and jump to Hyperspace before the Vader/Luke battle is finished. When Luke calls out to Leia from the antenna, there is no response.
Tatooine. The band plays Baroque music and dancers twist their bodies to the beat. Han is seen in Carbonite against the wall. Night falls, and a masked figure arrives and rescues Solo. ‘Who are you?’ ‘Someone who loves you’. Shot of the Falcon flying away from Tatooine.
The Rebel fleet is assembled. The plan to attack the Death Star is underway, and cuts before Luke arrives. There is a montage of preparing for battle and the shuttle goes into Hyperspace.
Luke awakens in Bacta. a sinister droid places a device against the tube and he ascends. Form cut to the elevator shaft with lights rising on its surface. It opens and Luke appears beside Vader. Together they walk into the throne room. Cut after ‘you will call me master.’
The shuttle flies past the command ship. Repurpose footage of Leia sensing Luke’s presence from ESB on the Falcon. He senses her as well from the throne room. Luke says ‘You’re gravely mistaken. Soon I’ll be dead. And you with me’. The Emperor makes his speech about his plan.
The shuttle lands and the troops file out. Cut straight to them opening the door to the bunker and beginning to set the charges. The Ewoks arrive as a surprise to everyone. The rest of the battle, and the film, plays out as in the original. I don’t know how Leia as Luke’s sister would fit into this, but perhaps it could be cut altogether.