For me some of the fresh introductions in ESB felt like they were going to go somewhere but didn't in ROTJ (presumably because Lucas felt out of love with Star Wars and what it over and done with).
One obvious example is Boba Fett.
A lot of work went into designing him.
His armour and his ship have the sort of detailing a comic book creator would put into a major new title.
He is clearly designed to be Solo through a mirror darkly.
If Solo was really as mercenary and cynical as he pretended in ANH he would be Fett.
He knows Solo's tricks and uses them to track him.
He truly is solo (he hasn't even got a sidekick like Chewie to keep him company).
It's a shame really he wasn't conceived as such when the first film was written.
He could have conned Greedo into confronting Solo in the cantina, he could have tipped the Stormtroopers off knowing that Solo would escape but just to be a thorn in his side.
When he turned up again in ESB the audience would then be tempted to ask, what's the beef between these two? It's not just a common bounty/hunter relationship here. Has he got some sort of personal grudge?
I know some people will find this galaxy shrinking but ROTJ had a opportunity to show how far Solo had grown and where he may be going (joining the Rebels full time, contemplating settling down with Leia etc) by showing what he could have become through Fett.
I suggested a fan edit scenario where instead of being a bodyguard waiting around to get killed in Jabba's palace Fett worked the Rebels and Empire off each other.
He is hired by Vader to lure the Rebels to the Death Star trap and hired by the Rebels to track the Emperor's movements.
Both gigs giving Fett the information he needs to pick up both paychecks.
If it were actually filmed back in the eighties rather than dropped in a fan-edit insert you could have a confrontation where Solo gets a chance to get even with Fett but doesn't.
Solo could instead (in his smart mouth way) question Fett about what the money is all for, which would mirror Luke trying to get Han to help the Rebels in ANH.
Something like :
Han : "That's a lot of cash Fett, what do you need it for alimony?"
Fett could walk off but without looking at him say "Yes".