But, when you consider the fact that we already know Oliver is going to be helping The Monitor (who can interact with people in all of the worlds and timelines of the multiverse) try to stop the coming crisis (which will lead into the multi-episode Crisis on Infinite Earths event), it doesn’t seem so impossible at all that some timey-wimey, multiverse shenanigans will lead these women to a place / time where they can band together on a regular basis.
Arrow has 10 episodes to tell the story of its final season and set these crime-fighting ladies up for their own series, and that might not seem like enough.