..sci-fi isn't regulated to the distant future, dystopian settings aren't limited to some apocalyptic fallout. This film was set 20 yrs from now (basically, a blink of an eye forward). Given the current state of this world, this story doesn't seem so far fetched.
I actually think the director made the right choice to do away with all the bells & whistles typically associated with sci-fi and focus more on the actual grit.
4. "...thats where im at too...." In response to Reply # 3
i actually didnt know ANYthing going in (other than it was Kaluuya's directorial debut)...so i went in blind. Didnt know it was going to have any "SciFi" elements at all...so, i actually totally DUG the 'subtlety' of the "scifi" treatment here, i feel the 'scifi' wasnt supposed to be 'the story' here....instead it provided a nice, and i felt interesting 'texture/frame' for the true core & essence of the actual story to exist within...