Of course, when that was the case it was being rumored that Batman movie would have several villains in it.
It was once rumored that a large part of the Batman standalone movie would be set at the Asylum.
Arkham Asylum has been a much more important location in the comics and the video games, where one entire game was placed on the grounds of the Asylum.
While it’s unlikely that Arkham will make for a major location in Justice League, it could be a sign that things are being set up for the future.