This article reveals why Aquaman will appear in the Batman vs Superman film, I wouldn't call it a spoiler but who knows.
Maybe the appearance of Cyborg doesn't mean he will be in the JLA movie, perhaps he will replace the role of Guardian in the Superman story lines/films as a representative of STAR labs and not to appear as though they are copying Captain America's character.
Aquaman appearing shows me that they want to go with a more classic cast for that movie, which means it will be rounded out with The Flash/GL and possibly Martian Manhunter.