Well first of all, Matpat is describing a theory for Episode VII, which was all know to be false since since he is still a Jedi and only has about 20 seconds in the whole movie.
But I could see Luke going to the dark side momentarily in Episode VIII, but maybe not permanently. From Episode VI we know that Luke does dabble a bit in the dark side but never truly goes over... he is still a Jedi. I think we will continue to see this struggle in Episode VIII between the light and the dark inside Luke.
But will Luke go full Sith on us? I doubt it.
I know it's cheesy, but I feel grate