It's already been planned out.
I actually find it hard to understand the number of people that believe there was never an overall plan to this trilogy. (despite Rian's quote from before he started) Like they just handed it over to Rian & let him do whatever he wanted with their 4 billion dollar asset. Meanwhile, they're over there micromanaging Solo & firing the director for creative differences. I think that quote may have been before they briefed him on their direction. Maybe they said... "here do whatever you want" just to see what he would come up with... but in no way was that freedom of choice not retconned by the story group that he physically moved in with for 4 months while he was writing the script.
I believe the details were allowed to be altered & made up on the fly... but no way they didn't have a clear road paved out. Lucas even mentioned that they layed out all their intentions to him shortly after the sale.
No way did they kill the Jedi order which is at the heart of the whole mythology just because that's what Rian wanted to do. No, that came from above, just like Disney doesn't want midichlorians to enter into anything Disney makes. So everything that happened in TLJ has a purpose & a plan toward the whole. I feel that they could've given more answers in TLJ... but when they looked at the whole... for whatever reason... they decided to make this end stone cold & hold the answers off for the finale.
I'm almost 100% convinced that Snoke is Darth Plagueis. As the resistance keeps saying... that "there's only one more movie... & how are you going to answer all these questions in one movie." Well with just a few minutes of screen time you can introduce an entire backstory that encompasses all 11 films & brings everything to a nice continuity. From there we still have another 2 hours of movie left for everything else to fit neatly into that world.