A lot of Rian Johnson's latest interviews seem to indicate that the new trilogy he's working on after the "sequel trilogy" wraps up will be something stand alone.
Could it perhaps deal with the Old Republic? Not necessarily say, an adaptation of the games/Tales of the Jedi/Dawn of the Jedi/Darth Bane material maybe, but perhaps something new based on what we know from the films/cartoons canon etc-that the Jedi and the Sith once had an ancient war of some sort, which reduced the Sith-who once "ruled the galaxy"-to the rule of Two. Such a series could also explore some of the material Disney's added to the canon; the "First jedi temple" could perhaps come into play, although presumabely in a better state (...and I'm guessing we're going to learn a lot more about that in a few weeks)-or the Disney canon version of Malachor. Maybe even the Knights of Ren and whatever Snoke came from, if they're relevant somehow.....and of course, maybe one of those KOTOR Sith Lords could be put back into canon. (Except for Bane, he's pretty much already still canon anyway).
It's kind of what some fans wanted to see in the prequels-massive armies of Jedi vs Sith, instead of the Jedi vs. Robots stuff that we got......(I think that's in part why KOTOR appealed to fans in the first place as well.)