Here's my idea for the Had Abaddon thing… How about the entire Death Star II idea is ditched, instead, the space battle would take place near the surface of Had Abaddon's capital, with ships doing attack runs on many of the Imperial Buildings. (Maybe Lando could enter the Imperial Palace and destroy it's Power Core?) But to bypass the planet's shield, Han Solo and his gang have to disable the Shield Generator located on the planet's forrest moon (Or it might make more sense if the shield generator was located on Had Abaddon, but in one of the few forests left on the planet. You could add traces of the Empire starting to industrialize it, thus forming an "Ewok/ Lorax" kind of thing) The Luke battle will take place in the Imperial Palace in the Emperor's Personal Throne.

It's a very rough concept but the only major changes would be re-shooting the space battle with models, but now Endor doesn't need to be altered too much…