As convincing as that video is, I still think it'll be more a situation of Luke grappling with both the dark side and the light, rather than him being downright evil. The whole going-into-seclusion thing feels like him knowing how dangerous he can be, so he essentially attempts to remove himself from the equation completely. He doesn't want to cause any harm, he doesn't want to sway anyone else. Which wouldn't be the actions of someone who has straight up chosen the dark side.
That said, I just thought of a pretty cool twist... what if Kylo is after Luke's lightsaber not for his own gain, but rather because he wants to return it to Luke? Maybe it was even Luke who sent him on his mission. How crazy would that be to think Kylo is after Luke's lightsaber for some nefarious personal reason, only to see him deliver it in person to Luke in the final scene?
That said, I just thought of a pretty cool twist... what if Kylo is after Luke's lightsaber not for his own gain, but rather because he wants to return it to Luke? Maybe it was even Luke who sent him on his mission. How crazy would that be to think Kylo is after Luke's lightsaber for some nefarious personal reason, only to see him deliver it in person to Luke in the final scene?