The following contains spoilers for Justice League.
A lot has been made about the fact that Ben Affleck probably won't be hanging around the DC movie universe for the long term. It seems that Justice League may have begun to sow the seeds of his eventual departure even sooner than we would have guessed. Justice League is very much Affleck's movie, he's the lead as much as anyone is in the ensemble, and some of Bruce Wayne's time on screen seems specifically dedicated to explaining that he won't be around forever, and setting up future Justice League movies to have a different team leader.
In a scene near the mid-point of the movie, while the Justice League is discussing whether or not to take a particularly contentious course of action (not touching that, even with the spoiler warning), Bruce Wayne and Diana find themselves on opposite sides of the topic. The pair gets into it, leading to Wayne being critical of Wonder Woman for her self-imposed exile. He wonders why he'd never heard of the powerful demi-god until a random photo happened to surface. It's clear he thinks Diana could have been a major force for good for the last hundred years if she'd been willing.
This gets followed up on later, when we see Bruce Wayne taking a bit of a break from the rest of the team in the back half of the film. Wonder Woman comes upon him and sees the bruising that has built up on his body over the course of the film and, one assumes, even longer. The two begin to talk about how much Bruce Wayne has been putting himself through and Wayne is fairly candid that he's not exactly sure how much longer he can keep going, he even questions how well he's handling it now. The pair then discusses their earlier altercation and Bruce Wayne explains that the reason he was so critical of Wonder Woman is that he sees her potential as a leader of this team, something they will clearly need at some point. When he's not around, he wants her to take her place at the front of the Justice League.
This line clearly isn't an accident or a time filler. While it's hard to tell whether this particular scene was part of Justice League's reshoots, since it doesn't include obviously terrible CGI, in a film that was trimmed down significantly, this was left here for a reason. As it stands now, we don't even know for sure if Ben Affleck is going to hang around the DC universe long enough to make the much-discussed solo Batman movie.This line was put in specifically because Affleck will be gone sooner rather than later.
And it makes sense that Wonder Woman would be the one replacing Batman at the head of the Justice League. Considering how popular a character she is, her movie is at the top of the DC universe from a box office standpoint, making her the focus is obvious. More than that, however, she appears to be the true moral center of the team. While that role is traditionally filled by Superman, for good or ill, the film version of Superman is not the same sort of character that we traditionally see in the comics. Based on Wonder Woman's solo film, she's clearly the one who sees a bright side to humanity that's worth fighting for, which is what the Justice League is there to do.
More than likely, as the DC universe moves forward we'll start to see Gal Gadot's Wonder Woman take a more prominent role, and Ben Affleck's Bruce Wayne start to move into the shadows. Since this shift could even happen before Justice League 2 ever happens, this moment from the new film sets it up so that transition will make sense when we see it.