In my fantasy world, Finn and Rey are both force sensitive (you don't have to change the first movie at all), they both go to Luke for guidance in TLJ.
Luke doesn't want to train them (he can still be a hermit). Only kinda does, Rey does her Rey thing with Kylo (rey is obviously gifted in the force), eventually leaves to confront or "save" kylo in the middle of the night. Leaving Finn.
Exact same throne room thing happens. Except at the end... Rey stays and is turned to the Dark Side with Kylo.
Luke realizes he F'd up (again)... Finn is dismayed losing Rey or whatever... Luke decides he needs to train Finn in order for the resistance to have a chance.
Movie 3.... Kylo + Rey vs Luke + Finn
I mean, damn... Finn would have been a PERFECT Jedi. Dude didn' twant to slaughter people as a stormtrooper. He already has the "anti violence" monk thing going for him.
Fun times for all!