In an already crowded movie with the three biggest DC Superheroes coming together for the first time plus two new heroes who haven't had an movies, Batman V Superman is looking pretty crowded. Batman, Superman, Wonder Woman, Cyborg, Aquaman, A possible Robin in a flashback, Lex Luthor and the mysterious new threat that will arise. As crowded as that may be, apparently there's two more on that list.
Batgirl (Jena Malone)
That's right, rumor has it that Barbara Gordon will make an appearance as well. First known as Batgirl, Barbara Gordon was a part of the Bat-Family and was pretty awesome too. Until Joker came along and ruined the fun by paralyzing her and putting her in a wheelchair. Her superheroing wasn't over though. She continued to aid Batman in the form of Oracle. Kind of like an informant.
KG Beast (Callan Mulvey)
KG Beast is rumored to make an appearance as a villain. You may remember him from Arrow Season 2 Episode 4. Or you might remember him from Justice League Unlimited. Either way, he's a Russian killer who's also been part of the Suicide Squad. This could help tie in to the scene of Superman holding that Russian rocket from the trailer.
Is this... Good?
This may be a problem for the DC Cinematic Universe. I personally think Batman V. Superman will be amazing, but all these characters in a two-hour movie? There will be pretty much no character development if they go this way, although KG Beast can manage without it. Batgirl however, is a major character in DC Comics and if they introduce her in the universe, than I'd hope they give her proper development.