I don't think they're changing the entire plot. Kasdan isn't going to boot one set of directors for not following his script closely enough for another that will come in and do the same and a plot change would require a rewrite which they don't have time for and I doubt Kasdan would be inclined to do. As good as he is at writing he says he hates the process of it and he's not known for knocking out scripts in record time. A greater emphasis on Jabba could very well be a way of streamlining the remaining production by condensing a couple of other players into his role.
Strongly disagree with your wording and language there. "Greater emphasis?"
Its a major addition, and very likely signals a plot change with the level of development of Jabba they are talking about.
Howard is expected to reshoot much of the film in which Hutt only enjoyed a cameo appearance.
Cameo to star. The language and implications are very clear here. Greater emphasis on a cameo is exactly what we are not talking about here.
How do you put greater emphasis on a cameo?...
As for the plot change itself, I was pulling for Joss Whedon (someone who actually gets Star Wars and has directed Star Wars-esque adventure movies) and had thrown it in the garbage on announcement of this swap, but if Howard is reshooting and rewriting much of the movie with Kasdan-- I'm down again.
Lord and Miller were obviously taken off the project because Kasdan signalled a complete change of tone and story for these so-called "reshoots". Its all a lot of gas to protect Lord and Miller and let them go with professional courtesy.
Fact is, Kennedy told them they were doing big revamps of scenes with another director. She said you can keep your name on the movie if you go along with it. Lord and Miller said no we can't do that because then its not our movie. That was the end of that.
Now we further find out that Howard will be making some drastic changes with a new additional character (Jabba). Howard is a veteran, Kasdan is a veteran-- we can guess now in light of this Jabba development that they are doing some rewrites together with mutual respect. Howard likely suggested if we are going to spend money, lets spend it right.
This could very well amount to a new movie.