Let's face it! It's too early for a Justice League movie. So let's now focus on how to lay down the foundation of that movie.
In my opinion, the best way to do this is through the Man of Steel sequel. As was shown in the Man of Steel, different characters in the DCCU exist in the same world (like the satellite which confirms the existence of Bruce Wayne). While it may be too early for a Batman reboot, it would make sense to atleast introduce him in the Man of Steel (MoS) sequel.
There are a several plot scenarios which may allow this. One of which is if Braniac will be included in the MoS sequel. Superman can match his strength, but while Superman is not stupid, he might need the assistance of an almost genius level Batman to counter every one of Braniac's plans. Also, Wayne is probably the only person who could supply the tech which might be necessary to stop Braniac.
If you don't like to place Batman in the MoS sequel, there could be several heroes to choose from. Like Flash, Manhunter, Wonder Woman, GL, or Aquaman. I think it would be great to see Superman seek Manhunter for assistance. Their role need not be that long that it looks like it's their movie, but their assistance must be so necessary in a sense that Superman cannot save the world without such help.
OR since, Superman battles create so much collateral damage, another hero gives assistance in keeping the civilians safe from harms way as Superman neutralizes the threat.
I couldn't really think of a complete story line right now, I just had this thought the other day and wanted to share it. IMO, it would be great story wise and would lay the foundation for a Bigger movie like the Justice League.