Depends how much retcond they do. I don't think they will do to many maybe Rey's background.
According to Rian Johnson they had no overall story arc. JJ wasn't the original plan.
JJ made a bit if effort in TFA to weave in plot hooks for future movies. It seems he will have to make the most of what he can do.
Just based on the trailers it's why I think anything they do will feel rushed or the explaination is going to be weak. They have a lot to cover for example.
How did Palps survive?
Why has he been hiding for 30 years?
Where did he get his Uber fleet from?
Where did the resistance get their fleet from since they were crushed?
How well they introduced the two new characters?
Rey's background was Kylo lying?
Kylo/Rey's relationship in a way that's not ham fisted.
More superweapons?
Is the ending a rehash of RoTJ?
Etc that's just a few basic ones. I suspect a lot if it is doesn't matter or just because?
I mean... A ton of those are just Star Wars tropes at this point.
Superweapons? Check
Secret vast fleets hiding in preperation? Check
Some bad/good person lying or omitting important facts? Check
People not actually dead when we all thought they were? Check
The most important question I want answered is this: If the movie does well and you like it Zard, will your spirit finally be at rest and can move on?
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I have to say, I was already excited about the movie, and now after seeing that clip Morrus posted, I can't wait. I knew there was a reason I was keeping away from Star Wars stuff until next week.
My bold claim.
With this newest information, I think... movie will tie things back together. With Palps having pulled on the strings from wherever he is hiding, forces will rise to stop him. Those allies of Leia's who didn't answer before still remember the tyranny of the old Emperor and finally heed the call to help.
Some awesome space battles are had. Some cool lightsabers fights take place. Sprinkle in some interesting but perhaps expected or hoped for conversions happen. BAM! The force is finally at equilibrium with a couple of Grey Jedi.