A dark Luke would be too interesting.
It's gonna be safe I'm sure. These theories of Rey Rey going bad or Luke being an antagonist is just hype BS. Luke is going to be a lame, goofy character. Just look at the trailers. There is absolutely nothing stoic about him. He looks shell shocked and frightened in nearly every scene where Rey is showing off her powers.
Look at his dialogue so far.
"I only know one truth, it's time for the Jedi to end."
"I've seen this raw strength only once before. It didn't scare me enough then. It does now."
"This is not going to go the way you think!"
It's going to go exactly how we think. He doesn't seem like a very powerful or in control character to me. If he was, he wouldn't have become a hermit and let all this dumb crap with the First Order happen, He ****ed up with Kylo Ren, he's afraid he'll **** up with Rey. He's going to be a sad, hollow shell of his former self. Already we see he's cynical and unheroic. They've been promoting Luke as "a character that the protagonist meets that isn't the hero they thought he once was" and Hamill himself saying he disagrees with every choice they've made for the character. Why anyone would expect great things from him is beyond me.
Now I don't think they'll go as far as making him a bumbling idiot that just happens to be the mentor character, but I don't expect anything great from him. As an audience, we've been getting warnings not to expect much from Luke. They hyped up Hamill's return, only to have the character show up at the very end for the last 30 seconds of the movie. His character literally pussies out and goes into hiding and seclusion, and you guys expect his character to suddenly get into the spot light and become something as important as the main villain? At best he's a Yoda or Obi-Wan knock off, at worst, he's portrayed as a spineless fool that Rey has to build up and show the light to before he's finally pulled off the stage.
Don't think it's misdirection personally. These new lame movies aren't about Luke and the gang. It's about Rey, Kylo Ren and maybe Finn. Han was just used as a vehicle to guide Rey into her journey and make Kylo descend into his. Leia and Luke will be no different. Look at Leia, she's already being promoted as this sacrificial lamb for Kylo Ren's characterization. "Ooooooooh, is he going to kill her or is he going to spare her."
Who cares.
My friend was actually texting me telling me not to spoil anything for him. He does this for almost every upcoming blockbuster flick before he ends up spoiling himself. What's there to even spoil? I'm thinking back to 2015 with Force Awakens where everyone was caught up in "muh mystery", "muh revelations". What ended up happening? What did we find out. Kylo Ren is the son of Han and Leia and Han dies. Big whoop. Both those things were being speculated when TFA was still in production. You didn't even have to follow the series to know that Han was going to bite it when that's all Ford talked about when he was promoting the movie or all those pics of Kylo Ren without his helmet.
I'll never understand why people torture themselves or have fun with it. It's become soap opera tier. This is some people's 8th Star Wars outting and yet they still expect to be wowed and surprised by some "I am your father" tier revelation. That's never going to happen again, not when everything leaks, everyone's speculation is made available in real time and they always go with the safe, predictable out come. It reminds me of Harry Potter fans. "Ohhhhhh the boi who lived dies and all the wizaahds went bad and died." None of that crap happened. Everyone was happy on that stupid train station or whatever the ****. It's always a cop out, a happy predictable ending.
What you see is what you're going to get. Snoke is the big baddie, Rey is the hero, Kylo Ren is a flawed villain, Luke is the defected advisor and everyone else are distractions from the main plot. Sure, there will be a couple of surprises, but by 2018, we'll all be asking questions and waiting to get disappointing answers by the time the hype and wait for Episode 9 comes around. It's the same thing every year.