I had a few thoughts about reframing the political situation in the Sequel Trilogy.
In TFA, the opening crawl could say that the galaxy is pretty much divided between the New Republic and the Imperial Remnant/First Order, and there is a fragile peace between them. The Resistance is an independent movement, led by Leia, that operates within First Order space (the Resistance name makes more sense in this context as well).
Starkiller Base will not be a super weapon. Instead, Act 3 will be focused on rescuing Rey, and also getting the other half of the map to Skywalker (the oscillator will instead be a planetary tractor beam that must be destroyed for them to escape.) The New Republic will not be attacked or destroyed by the First Order at all. Their goal right now is 1) maintain control over their territory, and 2) destroy Luke Skywalker.
TLJ would continue the story by showing the First Order trying to destroy the Resistance before they can get Skywalker. The New Republic cannot intervene because it would break their treaty, and this could possibly be mentioned in the crawl. Rey mentioning the First Order taking control of all major systems within weeks would be removed, as well as other lines that contradict this new idea.
In TROS, the return of Palpatine and the massive Sith Fleet is what prompts the New Republic to finally join the fight in the climax of the film. Other small adjustments would be made throughout to work along with this idea.
The major con of this idea is that the New Republic still existing offscreen throughout the films might lower the stakes of the trilogy. The First Order taking over the galaxy is a big deal and the last good guys being a small group of people makes their struggle more of a challenge. On the other hand, having the New Republic exist offscreen would allow the Sequel Trilogy to not undo the victory of the Original Trilogy heroes, as some feel it has. Basically, the threat of the New Republic being destroyed would be moved to the last film by introducing the Sith Fleet. Kylo Ren and the First Order want this fleet in order to take over the rest of the galaxy.
I also think the idea of the Galactic Civil War ending in a truce or stalemate makes a lot of sense. The idea of the Rebellion, which still seemed small in ROTJ, was able to defeat the entire Empire in one year feels somewhat convenient, even if the Emperor did die. They would still have so many more resources at their disposal, but I could see the power vacuum and subsequent infighting would’ve allowed the Rebellion to liberate hundreds or thousands of systems and then to negotiate with the Remnant once they finally coalesced. The First Order is the remaining territory of that Remnant, so the story becomes more about finishing what the Rebels started in the Original Trilogy, rather than moving everything back to square one.