For those of you who do not know what a crisis is, a Crisis (or at least a DC crisis) is usually a story that revolves around alternate universes, and occasionally changes continuity. Ex: Crisis on Two Earths, Crisis on Multiple Earths, Crisis on Infinite Earths, Infinite Crisis, Final Crisis, and Flash Point.
Now given then news, that all DC superheroes exist in their own universes, is it possible that the point of a Justice League film, is to combine those universes to create single DC film universe.
This is all speculation, of course, but in many aspects this could work, keeping a DC feel, introducing a Universal threat, such as Anti Monitor or Krona. This concept also opens many opportunities, such saying that all films related to DC are in the same connected, like Superman 78 is an is earth 2 superman, and so are the Burton Batman films. Smallville could be a Superman Earth-One type universe.
This is just a concept, only speculation.