The origin of Snoke and the First Order.
Just because Star Wars 9 will be the end of the trilogy does not mean that it's the end of the line for the Star Wars franchise. There's a lot to look forward to with Rian Johnson's new trilogy as well as the standalone movies. However, it would be nice to see J.J. Abrams explain how the First Order came to power while addressing who and what Snoke is all about. The next installment sees the Resistance down to depressing numbers and they're going to have to rebuild while the Resistance is still whole. Maybe Abrams can shed some backstory on the First Order while the Resistance rebuilds and gains new recruits inspired by hope and the myth of the Jedi. To take the First Order and relegate it to books or video games would be a terrible disservice to fans.
Rey and Kylo Ren.
This is a no brainer here, but this will have to be addressed in Star Wars 9. There were a lot of implications on the relationship between Rey and Kylo Ren and one can see Ren's reasoning to start something brand new. But Rey believes in the Light side of the Force and believes that the Jedi can live on. The beginning of The Last Jedi sees Kylo Ren wrestling with his feelings and being torn between the Light and Dark sides, leading to an amazing plot twist. Kylo Rey kills Supreme Leader Snoke and offers Rey a chance to start over, but she declines. Regardless of what happens in the next installment, Kylo Ren's thirst for power will have to be addressed and that will undoubtedly involve Rey.
The Resistance vs. The First Order.
There is a galactic civil war going on and although the Resistance has been torn apart, news of their victory and the return of Luke Skywalker will help to rebuild the recruits. The entire crew of the Resistance can fit on the Millennium Falcon and that's just plain sad. The young boy on Canto Bight (Broom Boy) is seen with the ring of the Resistance, signaling that hope is not lost and that the Force can flow through just about anybody. The First Order will more than likely continue to be led by the odd couple of General Hux and Kylo Ren, but it seems that Kylo Ren will exert more power to keep the takeover going. But will Hux learn the truth about how Supreme Leader Snoke was killed? It's going to have to be addressed again sooner or later.