Meh, I am okay with them not being in TLJ. Not every bread crumb need to be answer ASAP. It makes perfect sense that Kylo doesnt have them around Snoke. Rule of two would eliminate them or get in Kylo's way of being Snoke's student.
Now that Kylo has successfully pulled off a coup, he has his own loyal followers to install. Or there are 6 wild cards out there. Seeing Kylo and Rey are about to redefine how people are going to use the Force in the near future, having more semi trained Force users out there opens up more stories with the a Force beyond the chosen blood line of the Skywalkers. Balance was brought to the Force through the Skywalker line. For the Force to remain balanced and grow, such a powerful bloodline needs to go away. Ridged ideas of Jedi and Sith need to die or evolve.
They can still have Sith and Jedi, but they can also make new orders that don't follow the ridge structure of Using the Force doesn't require Sith or Jedi- it just needs one to understand what the Force is and practice.
That is what both Luke, Yoda, and Kylo realized- the path of the Jedi and Sith are just social constructs. They are not the only way to the Force.