This is kind of fun! Not only suggest what kind of changes via FX and the like, but the actual flow of scenes!
Here is how I would cut JEDI:
(1) pan from the opening to the surface of Tatooine and play from the beginning with 3PO and R2. You can slim 3PO's lines (maybe), but Jabba still needs an entrance. You can alter the "Jabba behind the curtain" scene through editing (as described in an earlier post), as well as edit out the Lando reveal.
Add some FX to smooth out the Rancor, electrify the door as Luke tries to force-open it, even showing Slave-1 taking off in the distance and add Jabba's palace in the background when we first see the sail barges (as if they just took off as opposed to have been travelling for some time). Make the Sarlaac even a little bit bigger (and without the beak), fix the "force kick" and everything else remains the same.
(2) Luke heads out to Dagobah and meets with Yoda only; I see no problem with cutting out Ben's conversation, as it comes across as more "mandatory" than needed - Luke can figure out through the Force and his own intelligence that Leia is his sister, much less the concept that after Yoda dies his final test to complete his training is to face his fears ALONE with no coaching from a disembodied spirit.
The conversation (with Yoda) ends with either Yoda confirming Vader as Luke's father or with the following line about "the other". Add the dramatic music from the Owen and Beru death scene to emphasise the fact that Yoda is confirming what Luke feared, much less that he is all alone to face Vader AND the Emperor and segway with either old Imperial march (per the segway at the end of Owen and Beru's death) or replace with the EMPIRE march and:
(3) the entrance of the Emperor and the new Death Star. Vader can either come down the ramp preceding the Emperor (as in he travelled with him as his chief hench man, ala Tarkin in ANH - which would allow the deletion of the useless red guards) or meet the Emperor as he was already stationed there. The beginning with Vader is rather redundant, as we get 2 more introductions to the new Death Star, including this one.
(4) Luke meets up with the rebel fleet and they prepare to launch their attack. Add some lines spoken off-camera (we see some reaction shots from Luke and Co. or other random troops) to the degree of "some of us have already infiltrated the base and will be waiting on the inside for your arrival" to indicate that this has been in the works for months as opposed to just that day.
Regardless, editing-wise the film would go along normally (albeit with the expected REVISITED style improvements). No Hayden; no morphing Hayden INTO the older guy - Ben and Yoda are not younger, so why would Anakin be younger, especially when he redeemed himself as an old man?
The main problem one can run into when editing sequences is complicating the storytelling process; JEDI is fairly straight-forward, and while editing could improve it, the film can get convoluted too.
(5) beef up the Ewoks with some sharp teeth and claws, maybe some Jawa-esque eyes (not so bright, but something to make them stand out, like the replicants in BLADE RUNNER - I think it would be really cool to see a shot with multiple Ewoks in shadow with "cat eyes" like the DEMONS poster); I like the idea of adding shrunken heads on their belts or staffs, maybe playing with their language to make it more gutteral and I guess "wookie-ish" - in fact, what if you had Endor as the moon of Kashyyk, and the Ewoks were off-shoots of Wookies (thus, a reason to make them more wookieish)?
Another idea: would it be possible to take all of the shots of Chewbacca (from A NEW HOPE, EMPIRE and even JEDI), alter them slightly and add in an extra Wookie or two so Chewbacca isn't the only Wookie there?
I'm getting off my own topic, but editing wise I would still try to keep it simple:
(1) Tatooine
(2) Dagobah
(3) Emperor, Vader and DS introduction
(4) rebel meeting
(5) fly to Endor and the rest follows
Chainsaw Ash:
I agree that there still need to be a hook - if you start with the Tatooine stuff (and all of it, beginning with 3PO, Jabba's introduction, Luke making his mysterious entrance, etc), you would directly follow up the end of EMPIRE (with them prepping to rescue Han) with them rescuing Han, which would be the hook.
No Vader entrance needed, since he can be introduced at the same time the Emperor arrives and we still see the new SINGULAR Death Star - no need to make this even more complicated than it already is.
Luke goes to Dagobah and has the most important thing taken care of (at least for the audience): Vader is confirmed to be his father and Yoda passes away, leaving Luke alone to "finish his training" and find out if he really can be a Jedi ON HIS OWN. Thus, no need for the Ben exposition scene. If this is about Luke's growth as a person, sooner or later the training wheels have to come off and he has to start figuring things out on his own and DEAL with them on is own. To have Ben, Yoda and OLDER Anakin to bookend the movie with their appearance to essentially tell him through their presence that he has succeeded is enough for Ben's involvement, since that is what Ben was training Luke for anyways.
In fact, I think it would help JEDI stand out of Ben was missing, making us feel just as alone as Luke (because if Ben doesn't make an appearance to Luke - visually or audioly - Luke is going to wonder the same thing we as the audience would: where is he? Is he truly dead now? Is he gone? Does he WANT to help? Maybe Ben CAN'T make an appearance because the Force has a will of its own, and has deemed that Luke MUST face this final test ALONE).