While there has already been some VERY adamant dissent and opposition to this equally new development, the inclusion of the character Cyborg in the upcoming MAN OF STEEL sequel also featuring Batman and Wonder Woman actually makes quite a bit of sense... maybe even more than does the inclusion of Wonder Woman, herself.
First, it ties the narrative into the first film in a way that is both reverent to the comics and will particularly pique target audience interest, whether they initially approve or not. As mentioned in one of the other MP articles I read on the casting, Cyborg is a product of STAR Labs, which is where Professor Hamilton works in the comics (Hamilton was featured and died in MAN OF STEEL).
Second, he could be a believable tie to either LexCorp or Wayne Enterprises (or both), even being a possible forerunner to a villain like Metallo given the technology angle. Certainly, a character like this might be perceived as able to take on a rogue Superman before that character switched to the side of the angels (so to speak).
Last, but not least, while I've never been a fan of making casting choices for racial or political reasons, Warner Brothers probably needs the good press that their inclusion of an African American superhero in their newest film property is likely to draw. Besides which, Cyborg has gained considerable popularity over the years and even those that feel his inclusion in a film like this to be premature based on comics history and so forth are probably, if secretly, curiously anxious to see how a live-action version pans out on the big screen.
I can't speak on the casting of Ray Fisher because, frankly, I have no clue who he is, but if he's really as new a face as another contributor's post claims, then I say it is all the better. With the few exceptions like Robert Downey, Jr. as Iron Man in 2008 or Tobey Maguire as the first live action Spider-Man in 2002, the trend of casting relatively fresh faces in superhero roles, which arguably began with Christopher Reeve's casting as Superman in the 1978 film SUPERMAN: THE MOVIE, is still one that seems to be respected to this day.
It has a number of benefits, the most obvious being that it allows audiences to focus on the performance and the character without the distraction of always being aware of who is behind it and what he or she is known for. Then there is the financial angle, which makes this even more feasible since these actors nowadays are generally expected to sign on for multiple movies. That being the case, their value goes up with each film, so the more money they can save on the initial casting, the longer they might conceivably be able to perpetuate and keep that actor in the franchise if he or she works out in the part. It sounds a little... cold... but it is generally true and something that benefits suits and audiences, alike.