This announcement has me less enthused than Arndt made me. Kasdan is so far past his prime. He hasn't done anything interesting since Wyatt Earp almost 20 years ago. Simon Kinberg just says "Meh" to me. He writes big action moviees, but nothing special. His "Star Wars" is what I picture as the bland "worst case" Star Wars of not bad/not memorable.
But I really wonder if this whole thing is real.
Here's the thing - regardless of anything else, it's pretty much certain that these 3 movies will have one central story-arc between them. IF that's the case, HOW do you start writing the second (and especially a third) movie BEFORE you've written the first one? I get where you might write the first one, get a finished shooting script, and THEN start on the second one before the first one is completed.
The only way this makes sense to me is if you are thinking of forming something like the Pixar brain-trust - call it the Star Wars writers room. More like a television series works, where you have multiple writers throwing out ideas, yet each writer is credited with a specific episode. I am not saying this would even work in Hollywood, but where they get together to hash out story points, and then each in turn "write" the script. (Even as I suggest it, I am thinking it's mostly a terrible idea.)
So, I'm write back to that this doesn't even really make sense to me. You really hiring a writer for a movie coming out in 7 years? That's like 14 Marvel movies away!