Star Wars: My Take
Friend at work has had me back down a Star Wars youtube rabbit hole. And with that comes alot of "why the Disney Trilogy failed", so unsolicited and unnecessary here is my thoughts and then treatment for SW: EP 7,8,9.
Balance
Star Wars is special because of the Jedi/Sith dynamic and the force. As much as Han is cool as shit and Threepio and R2 are amazing droids, people love Star Wars because of the Force. And each Trilogy has dealt with the Force and the idea of balance between the Light and the Dark sides of the Force. Or more generalized what is a good use and bad use of power. After the Prequel Trilogy you get Balance is equal numbers as influence there are 2 Sith and 2 Jedi Masters, the scales are "balanced" Light and Dark have the same amount of influence and actors. The Original Trilogy leaves balance as no Sith and one inheritor of the Jedi order, but this balance isn't about numbers. Its about the Dark side being a corruption and evil and it must be removed and contained. There is no balance when Evil and selfishness is allowed to prosper, so the Emperor and his Empire of Evil must be destroyed. But since this balance is acheived where can we go forward?
Forceless
Obviously the Galaxy keeps progressing after the Second Deathstar is destroyed. And there is a story to be told about the reconstruction of the Galxy and governemnt now that this massive power vacuum is left in the wake of the death of the Emperor. But thats not really a Star Wars story, even if it takes place in the same Galaxy, Star Wars needs the Force to underpin its tale. So while you want some story of the Galaxy that the characters inhabit it really isn't enough on its own without supporting the fairytale elemnents of Good and Evil, Light and Dark, Jedi and Sith, the Force.
New Balance
We need some way to have the Force off balance in a new way for two reasons; one we don't want to undo what Anakin/Luke have achieved so far and two we want a story with the Force as a major focus, without it being out of balance there isn't much conflict and we don't really have a movie let alone a trilogy. So that is the difficulty of the Sequal Trilogy. You have to unbalance the Force again, without destroying or undoing what was done before. *cough cough* bringing back Palpatine *cough cough*
Since the Force has been externally balanced I would look to a more philosophical balance of the self. The Jedi failed a new order needs to take root and it needs to decide how it will deal with attachements, or love. How do individual members struggle or deal with temptation. It is throughout Star Wars media, and it makes sense because as humans we all have our attachments and favorites and loves, but these aescetic Jedi are supposed to be aspirational? Do you really want to be devoid of romantic love or a sense of belonging and community, family?
Episode Seven: A Beacon of Light
The New Jedi under Luke Skywalker are seperate from the governemnt, a true religon and no longer state sponsored. With the fall of the Emperor force sensitive children feel more and more common, like when you take a weight off and then feel so much lighter, the universe is spreading good. Since the New Jedi have moved to distance themselves from the disaster that was the Clone Wars, Luke trains more force sensitives whereever and whenever they come into their power. Knights are much less common among the NJO, with only 1 in a hundred learning lighsaber combat, reserved for those of purest intentions and called only when aggressive negotiations are truly necessary. Concurrenlty Leah has been stitching together alliances of planets to reform a galactic federation. Due to the development of the worlds they cannot remain isolated and need a structure of trade and support to maintain qulaity of life for the sentient species, but at the same time worlds are reluctant to give too much power or control to a central authority.