As a Dark Tower Fan...
...I'm putting my whole two cents on the Roland-as-a-black-man opinion in the mix
Nikolaj Arcel has a small, if relatively competent filmography, so there's that.
The novel itself features Roland unquestionably as a white male, and in fact makes it a key dynamic in the story.
So let's say we decide to go Percy White on Roland based on the value of the actor. Idris has a high TV rating. The shows featuring him, The Wire and Luther, feature episodes with very high scores.
BUT...you put him in the cinematic universe where he is playing primary protagonist or antagonist and is not represented by an animated character, he peaks out at 7.8(not bad, honestly), but tends to hover more in the 7.0 or lower, with a heavy bible in the mid-6's and mid 5's.
This is nothing other than stunt casting, which didn't help the recent Fantastic Four at all, and helped eviscerate The Last Airbender. There is the idea in most minds that if the directors and writers will make a major change in the characters, they will disrespect more of the original author's vision of story and I suspect that here myself.
So, my forecast, even with heavy buzz and a huge fanbase, peak IMDB scoring will not have a sustained(week long) score of 6.7, and will(optimistically) settle in at a score in the low 6's.
Damion Crowley
Who knows but that, on the lower frequencies, I speak for you.--R.E.