Before we even learned the name of Star Wars: Episode VIII, it made sense that Luke would be a big part of the next movie, you don’t reveal him at the end of the last film and then ignore him, but that again would leave Carrie Fisher as a secondary player.
It’s a theory that many, including this writer, had almost immediately following Star Wars: The Force Awakens.
General Leia didn’t arrive until the latter portion of the story and Luke Skywalker wasn’t discovered until the very end.
That movie featured Harrison Ford’s Han Solo prominently, as a major character in the plot, right up until the end.