I asked myself this question roughly a year ago, and wound up writing an entire outline for a prospective Episode IX. Parts of it were very broad and generalized, while others were extremely specific. I wrote it half seriously and half jokingly, with the thought I was going to share it online...

Then my phone died and I lost that file forever. In short, based on the leaks, they're actually doing some of what I was thinking. Some. I employed a larger time jump (5 years instead of 1) and wrote Leia out of it. I think I made reconstituting the resistance a much larger plot point. I brought back the whole "prophecy" thing from the prequels and retconned Vader's death and redemption. Basically I made Vader Snoke, so that he died a villain in VIII instead of as a tragic hero in VI. The big bad of IX in my outline basically wound up being Hux, with him usurping Kylo as leader of the First Order.

Good idea? Probably not, but I think anyone who was tasked with writing Episode IX was going to have their work cut out for them. I don't think it's an easy nut to crack.