Obi-Wan Kenobi is one of the most important characters in the Star Wars mythology for many reasons, chief among them that he set Luke Skywalker on his path to become a Jedi. Luke's time with Obi-Wan was short, though, as the Jedi Master became one with the Force while being struck down by Darth Vader in A New Hope, but Obi-Wan continued to advise Luke from beyond the grave as a Force Ghost in The Empire Strikes Back and Return of the Jedi. So it stands to reason that Obi-Wan could have visited Luke once again in The Last Jedi, but according to director Rian Johnson, such a reunion wouldn't have been as emotionally satisfying since Luke would have been interacting with Ewan McGregor's version of Obi-Wan rather than the original Alec Guinness iteration. As Johnson put it:
Believe me, man. I would have loved to have had Ewan McGregor in the movie but it was just a matter of storytelling. The original relationship with Obi Wan --- obviously if Alec Guinness were still with us that would have made sense. But we never saw Luke ever interact with the Ewan version of Obi Wan, so there's less of the emotional connection and it might have been a little odd.
Ewan McGregor proved himself to be a compelling Obi-Wan Kenobi in the Star Wars prequel trilogy, but while it's one thing to bring back McGregor for a voice cameo in The Force Awakens, in Rian Johnson's opinion, the only way a proper Obi-Wan/Luke Skywalker reunion would work is if it was Alec Guinness opposite Mark Hamill. Unfortunately, Guinness passed away in 2000, and Johnson didn't indicate that there was any thought put into recreating the actor for The Last Jedi using CGI, as was done for Peter Cushing's Grand Moff Tarkin in Rogue One.
Warning: SPOILERS for Star Wars: The Last Jedi are ahead!
Yoda, on the other hand, wasn't an issue, as not only is Frank Oz still around, but as Rian Johnson told The Playlist, the crew was able to recreate the green whatever-he-is in puppet form to "kick Luke's butt a little." Force Ghost Yoda appeared right before Luke was about to destroy the tree containing the sacred Jedi texts, but Yoda decided to do the job for him, later saying that it's the Jedi's responsibility to pass along the Jedi knowledge to others, not books. I'd like to think that Yoda and Obi-Wan played a game of rock-paper-scissors in the Force netherworld to decide who would visit Luke.
It's possible that J.J. Abrams might feel differently than Rian Johnson and decide to bring in Ewan McGregor to play Force Ghost Obi-Wan Kenobi in Episode IX, but even if that doesn't happen, Star Wars fans could still see Obi-Wan return to a theatrical setting. It was reported in August that Billy Elliot's Stephen Daldry is in talks to direct an Obi-Wan Kenobi movie. However, with a Boba Fett movie also reportedly in development, it's unclear when the Obi-Wan movie would arrive.
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Star Wars: The Last Jedi is currently playing in theaters, and keep checking back with CinemaBlend for more news on Obi-Wan Kenobi's silver screen future.