The Future of Talia
I personally hope that either 1 of 2 options happens with Talia Al Ghul.
1. She is a ‘Black Siren’ type character and is still committed to Diaz and the villains but wants to work with team Arrow. So she kind of plays the double agent
2. She is on the Batwoman TV show and is a recurring anti-hero of the show and basically restarts the League of Assassins but as the League Of Shadows and has had affair with Batman, if the show continues for long enough and they delve into some Batman stuff, bringing in Damien could be really cool and a good way to connect Arrow and Batwoman.