My issue with Scott Eastwood is that he's not just too young, he's too pretty and soft. And I mean even outside that picture GNTLGNT posted. He'd almost make a better Eddie, but he's a bit on the old side.
I still think an unknown would be best.
Someone on a comments section said that if Elba is cast, they can change Detta's racism against Roland into castigating him as an "Uncle Tom" and refer to Eddie as Roland's white "massa", which would be an interesting take considering that at no point would the viewer see Eddie as anything other than significantly inferior to Roland. This...is interesting. It could even actually work.
That said, I still don't want to see a "reinterpretation" of Roland or this story. I want to see the book come to life. I don't always expect this, but when it's something well-loved by many (in this case including me) I strongly prefer it. Any time Hollywood has underestimated how loved a certain work is, they've ended up regretting it (witness the first attempt to film LOTR back in the late 70's or Demi Moore's feminist take on the puritanical The Scarlet Letter, or the adaptation of Susan Cooper's The Dark is Rising). The list is too long to go over here, but literally every time they've decided to take a classic novel with tons of devoted fans and adapt it into something that only superficially resembles the book, the result is a big, stinking bomb. Why do they keep doing it?
For what it's worth, Elba's potential casting is only the latest thing that makes me think they're gonna screw this up. There's also the mere fact of Ron Howard and Akiva Goldsman's involvement, the seeming rush to get this filmed, the comments I've heard about the different directions the screenplay will take, and the idea of casting Matthew McConaughey as the Man in Black.
"Well, Gunslaynger! How well ya fulfeel the prawphecies of owld! Whazzup, whazzup whazzup?"