Ian (or Rob, of course, though I know it most likely won’t happen) would be the only two actors that would make me watch the movie. They’re the only two that I could ever see as Christian. I haven’t read the published edition of the trilogy (or the ending of the story at all), but I would if they were cast.
As for Mark… IDK. Maybe. IJDK. Never really “pictured” any other roles other than Rob or Ian as Christian/Edward, and Kristen for Bella/Ana. To be honest, I can’t even recall who Jose was in the story.
The thing about 50 Shades, in my opinion, is that the characters were so obviously written after Edward/Rob & Bella/Kristen. Even though the subject of the story was far-reached, several of the characteristics, expressions, mannerisms, etc were obviously theirs… there wasn’t any “extra” descriptions to the characters that made them stand out on their own, unlike quite a few other amazing fanfics out there, that could separate the Twi-world view in the story, so I think it’ll be really hard to cast the roles with a lot of the fanbase knowing the truth of the origin.
Ian Somerhalder Casting “Fifty Shades of Grey”