One of the major criticisms that has been leveled at Star Wars: The Last Jedi, and its writer Rian Johnson specifically, is that it handled Luke Skywalker wrong somehow. That Luke's portrayal as a man who abandoned civilization to die alone was improper for the character. Whether or not that's true, it seems that Rian Johnson may not be the one to blame, as it appears Luke's decision was made back in 2013, before even Star Wars: The Force Awakens was made. At least, that's according to Christian Alzmann, who drew one of the earliest pieces of concept art of Luke for the new trilogy.
Christian Alzmann says that as far back as January 2013, before production on Star Wars: The Force Awakens had even begun, Luke was being described as "hiding from the world in a cave" like Col Kurtz, Marlon Brando's character in Apocalypse Now. This would seem to indicate that the version of Luke that we saw in Star Wars: The Last Jedi was always the one that was intended and this wasn't a case of Rian Johnson randomly going rogue.
It certainly makes some sense. At the end of the day, the fact that Luke Skywalker had removed himself to live alone on an island was a decision made in Star Wars: The Force Awakens and there are only so many reasons why Luke would have done that. Rian Johnson had to explain that decision and whether or not he was given the same description as Christian Alzmann or not, it's an explanation that makes sense.
Of course, the comparison to Apocalypse Now's Col. Kurtz only goes so far. Kurtz hasn't just removed himself from the rest of the world but he's gone crazy and built a cult to himself deep in the jungle. Luckily that's not what happened to Luke. That would have really upset some people.
The art itself isn't that different from the version of Luke Skywalker that we got in the film. Luke's a little better kept here, with his hair in a top knot like a samurai. He's a bit more monk-like, but he still looks like somebody who probably hasn't had much human contact recently.
Regardless of where the idea for Luke Skywalker's character arc came from, there will certainly still be those unhappy with it. The fact that Luke went away to die following making a terrible mistake with his nephew is still viewed by many as antithetical to his character, something which Rian Johnson continues to argue against.
Where the story goes from here is anybody's guess. Mark Hamill is confirmed to appear in the forthcoming Star Wars Episode IX. Whether that means we'll see Luke Skywalker again in flashbacks or as a Force Ghost is anybody's guess at this point.