Aquaman is an "interesting" character.
Actually he is not likeable at all as a superhero, since you simply can't care about him. There are better outsiders than Aquaman, so probably the main reason is gone.
Other than that he is a hero, who spends a lot of time under water, interacts with weird beings and characters and his backstory / adventures are not really something you can relate to. You simply can't. It's like Thor and Marvel.
But there are the Superfrieds and that really ruined his reputation. Now DC is trying to back him up to get rid of the bad image, since they obviously want to sell Aquaman comics, which are quite good by the way. The current on-going is better than Superman's and that is crazy.
In Injustice he will be a badass without a doubt, probably pretty much high tier, mainly because they will try to simply make him badass and likeable. I would still wonder if people would actually stick to him, rather than play with characters they like more.
Expect Superman, Batman and Joker to be the most used characters online! Up to a specific rank of course.