What if Kylo Ren turns against Snoke and Luke?
We all know that Kylo is a complicated character. We know that he looks up to Darth Vader.
We know that he may soon realize Snoke is using him (as Han Solo tried to push and I'd guess Leia will try to push in The Last Jedi).
So say that Kylo Ren finally realizes that Snoke is only using him for his powers. Because of this, Kylo Ren decides that he turns against Snoke.
But he's not running back to Luke or turning back to the light side. He left Luke for a reason obviously and the reason may become clearer.
He also believes that Luke was just using him for his potential and powers. So he becomes apathetic to both the Dark and the Light.
Kylo Ren gets his Knights of Ren to follow with his new beliefs creating his own small army. Perhaps he trains a new batch of "gray jedi" that aren't light or dark.
He duels Snoke but Luke and Rey show up. It becomes a three way duel with Luke and Rey vs Snoke vs Kylo Ren with Snoke's guards fighting against the Knights of Ren Kylo Ren brought with him.
In the end Snoke dies but Kylo Ren gets away and Luke and Rey leave as well.
Kylo Ren then begins to purge the galaxy of the Jedi and people who potentially could be a threat to him.
He hunts down random people who can use the Force, Luke's Jedi, and other small Force using groups and cults.
He convinces people across the galaxy that Force users have been the cause of suffering and pain in the galaxy for thousands of years through the Jedi, the Sith, the Empire, the First Order etc.
all great atrocities have involved Force wielders and groups typically as leaders of the factions. He rallies up a personal army and makes the Knights of Ren a threat.
This leads up to the next inevitable trilogy involving the New Republic and the New Jedi Order fighting against Kylo Ren's personal army.