It was an homage to the late Dwayne McDuffie, I believe. Justice League Doom, a film made back in 2012, was based off of a JLA comic McDuffie wrote called the Tower of Babel. In the adaptation, Cyborg was added as a cast member and as a JLA member at the end. The film as a whole was dedicated to McDuffie and a documentary was put on it dedicated to him as well. Suppose DC is just honoring one of it's greater writers through adding Cyborg as a member in the reboot. Plus, it adds a bit more diversity to the League's genesis (from a human perspective, not an aliens, because yes, a Martian would be a more diverse choice than Cyborg, however, they wanted to make it a mostly original lineup as opposed to carbon copying the 2002 JL series.)
As an afterthought, this design looks like it was really from a superb animated series. Very well done
For the sake of a reboot, Martian Manhunter is no real loss in my book, but that's me. In all honesty, the new 52 isn't as good as it could be on a lot of accounts. It seemed like a lot of purposeless reboots that really jump to about 400 pages into the novel instead of beginning again, almost like they're driving you to go back and read...the...original...comics...
...Clever, clever, DC.
Anyway, as to Cyborg, well, he helped save the world through the power of technology, something J'onn couldn't do. They did choose members that helped serve a purpose in the league. Even Captain Marvel-I mean, Shazam-played a part in JL: War moreso than Aquaman in JL Origins. So Aquafresh forked Darkseid's eye. Flash used a crowbar, and Shazam used Thunder, scoring a critical hit (Not Supereffective because Darkseid was like a Dark/Ghost type or something. Came out before Fairy type was introduced, so no supereffective hits for him)
Not a big fan of the new 52 & what they did to the titans & their histories, BUT, I do like your take on Cyborg. Simple yet stylish, instead of busy & cluttered like the actual new 52 versions I've seen so far