I do know he had some pretty big ideas. He was planning to work at them all simultaneously in case certain elements were carried over into the other films. General color correction. Fixing lightsabers. He spoke about voice dubbing. C-3PO wouldn’t appear until ROTS.
He mentioned before that he wanted to change it to where the Vader reveal would be saved until ESB, so it definitely would’ve required radical changes. Padme also would’ve survived ROTS, so that probably would’ve been something similar to what Hal did.
Here was one of his biggest quotes regarding that:
2008-12-05, ESBR Thread:
“When i first planned on doing the saga i wanted to bring the saga together as a whole and not have the PT >ruin many of the surprises in the OT, namely Leia being Lukes sister and Vader being Lukes father. I want >them to be able to be watched in chronological order. So in ROTS you will not have Anakin named as Vader or >even see him don the costume. The last we see of Anakin is being led away in the life support chamber after it >leaves the shuttle. Leia will not be named either. Palpatine has Maul, Dooku & Grievous in the PT, so when we >see Vader in ANH we will just think that he’s just another henchman. We will hear mention of Vader in ROTS but >not connected to Anakin. And also the problem with Leia remembering her real mother but Padme dies in ROTS >will be fixed in the PT, so no changes are needed in ROTJ.
“There will be probably more work done on the PT than in the Revisited OT. I have so many ideas for the PT but >a lot of new FX need to be done to achieve this. I’m hoping that a new version of TPM is released before i get >to that movie with the new CG Yoda because the abomination that is the PT puppet Yoda just cannot exist in my >edit. I’m even thinking of building my own mechanical puppet Yoda to replace the one in that movie.”
But as you can see from the date, a lot of what he said was from 10 years ago, and I’m sure Ady had come up with new ideas and changed old thoughts since then. But you can tell he really wanted to change the Prequels to remain consistent with the OT. Obviously don’t blame him for not wanting to do it. He’s already put so much time into the OT: Revisited, and the amount of work his Prequels would need probably would be even more than what he has done with the OT. But he has inspired a lot of the people in the fan-editing community, so maybe others can take his ideas and run with them.
I’m curious about which characters he was planning to dub. I’ve always felt like dubbing is really difficult to pull off seamlessly.
While I think the most interesting thing would be to hear his ideas on improving characters/plot, I’m also curious if he had any ideas for aesthetic/music changes. Also, for some reason I thought I remembered reading somewhere the possibility of him adding characters. So yeah, definitely a lot of VFX work in general. But like I said, I imagine his plan was pretty dynamic when thinking about it after a decade.