IMO there's nothing they can do in IX that will please some of the core starwars fans. Unless they literally just play part 4/5 again they won't be happy. Even George Lucas said he can't do it.
They are a lost cause
They can however, still make a good movie and conclude the series well if they put heavy focus on giving Finn something relevant to do, delving more into Rey's character (not her piloting or force abilities, her actual character) , and develop someone into a formidable, vader level villain. We seen that Rey is not miss goody 2 shoes and is lowkey interested in the darkside of the force, and Kylo Ren is wishy washy as to his true allegience but will pop anyone on sight without any remorse. They need to do something with that. Give the main characters more time instead of adding side plots which take up like 30 minutes of the movie.