When Dev-Em stands accused of murder and one member of Krypton's ruling council proposes the death penalty, another speaks up in his defense, saying that death should not be used--because Kryptonians "are not barbaric, like the Thanagarians!"
Thanagar is, of course, the homeworld of (many versions of) Hawkman and Hawkgirl, members of the Justice Society who sometimes also hang out with Superman's Justice League. In the comics, Geoff Johns (who contributed to the plot of the Man of Steel prequel) is well-known for loving Hawkman, having reinvented the character in a way that resonated with fans for the first time in years. He's also a member of the Johns-written Justice League of America.
Nods like this, and the Blaze Comics reference that hints at the possibility of Booster Gold in-universe, have been promised by the filmmakers all along, with some fans hoping that the acknowledgment of other characters would lead to a full-fledged DC Cinematic Universe. It's hard to believe, of course, that Supergirl, Hawkman and Booster Gold would be the first non-Superman, non-Batman movies made in such a universe...but any or all of them could believably be inserted into a Man of Steel sequel or a Justice League movie.
And, of course, there's the possibility that tying Booster Gold into the film could also tie the DCU to television when and if Booster's planned Syfy pilot gets off the ground.