How about this? Harrison Ford is back for episode VIII, not as Han Solo, but as an older Kylo Ren who time traveled back from the future.

One way this could work is old Kylo turned back to the light and is now Jedi Knight Ben Solo. He travels back in time and teams up side by side with Luke Skywalker to face his younger self in an epic lightsaber battle and kills him thus preventing Luke’s death and saving the galaxy. The movie would then end with him fading out of existence.

Thoughts?