Another persistent rumour for the movie is that Aquaman's wife, Mera, the Queen of Atlantis, will appear in some capacity in Justice League Part One ahead of a further appearance in the hero's solo movie the next year. It's unknown whether she'll appear in a cursory capacity or will actually join the League (this seems unlikely given all the "Unite the Seven" marketing), but casting is expected to begin soon. So, if we hear about a name actress being added to the Justice League line-up in an unknown role, there's a good chance it'll be for this.