Please head to your nearest salt dispensary and grab a choice-looking grain first, but the rumor mill says WB/DC will be shooting a Justice League movie back-to-back with Batman Vs. Superman, turning them into one extended shoot, but truth be told this rumor makes a lot of sense.
As Latino Review points out, there are several reasons that point to a double-shoot: 1) the schedules of the stars involved, especially Ben Affleck, who it will be much easier to keep rather than try to schedule back for filming next year; 2) the multitude of heroes being cast, which seem more reasonable if they'll be introduced in two movies instead of just one; 3) there's also a rumor that Batman Vs. Superman will end have a cliffhanger ending, which WB/DC might theoretically feel safer doing if a sequel was ensured to be coming out the following year, but this is two rumors trying to support each other, so it's kind of tenuous.
So, yeah. If true, I think this is a very smart decision on WB's part. Feels weird typing it out like that.