Completing Kylo's Training
The thought of this has me wondering what such a task would involve. More lightsaber combat emphasis? Greater focus on his mental and telpathic feats? Both?
If we suppose that Ben turned to the Dark Side of the Force and became Kylo Ren shortly after the events of "Bloodline" then I think we can suppose that Kylo has been under Snoke's tutelage for six years (Not counting the years of whispering in his head and warping his mind since Ben was a child). Was Snoke really waiting six years just to see if Kylo would be "strong" enough to kill his father? If Luke had spent six years with Yoda, his power in the Force would have verged upon incredible. Why would Snoke wait for six years to complete Kylo's training unless he didn't trust Kylo and wanted to keep Kylo "below" himself (in terms of power)? Maybe he's afraid of him.
Some wonder if Luke might be reluctant to train Rey. I wonder if Ben may feel the same thing regarding Snoke. Reluctance. To me, his regret over killing his father was obvious. I think it's safe to say that Kylo Ren will make the journey to Ahch-To at some point. Whether for vengeance against Rey, or to capture her, or to find Luke himself.
If Kylo decides that he wants nothing further to do with Snoke, a journey to Ahch-To may possibly have entirely different motivation for him.