The biggest player missing on the team and (as far as we know) in Justice League will be the absence of a Green Lantern.
There are plans for the Green Lanterns to eventually debut, with Green Lantern Corps roughly dated for 2020, but rumors persist that one may appear in Justice League.
These rumbling were given more credence when a report had Hammer as a top contender for the role.
Ever since Warner Bros. announced plans to create the DC Extended Universe, there has been great interest in who would fill out the Justice League roster.