7) Nightwing
It was initially believed that Nightwing was set to show up in Batman V Superman, with rumours pointing to the former Robin having quite a tension fraught relationship with his former mentor. However, we’ve since heard nothing about this fan-favourite character factoring into the movie, and it’s unclear if he’s even going to be included in the DC Extended Universe (especially as Nightwing is expected to be the lead in a Teen Titans TV series).
While Justice League is no doubt going to be all about the team squaring off with a gigantic threat, seeing Batman spending even a little time with his former ally would be a nice way to remind us that he’s a man among Gods and far more comfortable back in Gotham City, which he could perhaps leave under Dick Grayson’s protection while he’s away fighting alongside his newfound teammates.