Marc Guggenheim said there would be big Arrow news today.
Word is that Katie Cassidy will be returning to Arrow as a series regular in season 6. She will appear in the final two episodes of season five, playing the Earth-2 version of Laurel Lance and then pick up with that in season six. Which gives the team 2 versions of the Black Canary (one being Black Siren). She will also be appearing in the season finale of Legends of Tomorrow.
Executive producer Guggenheim had this to say about Cassidy's return:
One of the things that most excites us about Arrow is that we go where the story takes us. Last year, the story took us to the tragic death of Laurel Lance. This year, our midseason finale reintroduced us to Laurel's doppelgänger, Black Siren. We were so taken by Katie's fearless interpretation of this character that we knew her story was not yet finished. We couldn't be more thrilled to welcome Katie back to Arrow as Black Siren, though as her appearances on Arrow and DC's Legends of Tomorrow this season show, she never really left the family.
So, what will the show do with two women in Oliver's life that have sonic powers. Does this bode ill for Dinah Drake (Juliana Harkavy)?