What do you think the plot of the next (2019) Star Wars movie should be exactly?
Certain plot points are a foregone conclusion. Kylo Ren will face Rey to 'atone' for his actions during his fall to the Dark Side. My guess is the Resistance will have some 'last chance' operation to stop the First Order and, while Poe, Finn, Rose and some new heroes, carry out that assignment, Rey will sneak away to have her final confrontation with Ren.
I would venture a guess that the Knights of Ren may show up in some capacity, probably engaging the Resistance forces in their operation, and, at the end, there will be some type of acknowledgement that Rey will restore a new Jedi Order, or something in the same vein.
I think it would be silly to have Kylo Ren redeem himself as Vader did in ROTJ. I'm hoping he faces atonement for his actions and that stories proceeding from there can focus on something other than the Skywalker family. That story arc has been done, its time to expand into the larger galaxy and see how the Force, and the past, affects other individuals moving forward.
Based upon the naked cut-and-paste of plots from the original trilogy in the last two films, I am fully expecting that we can look forward to a plucky band of rebels going down to a moon to try and shut down a shield generator protecting yet another Death Star type structure with yet another inexplicable weakness that will let a single skillfully piloted fighter to destroy it.