Board Thread:Show-Related Questions and Answers/@comment-26569765-20160515144204/@comment-24674051-20160524165200

I realize that Killian was not part of season 1, and did start as guest/recurring early in season 2 (2x4 I believe), by the end of season 2, he was in every episode and was promoted to regular in season 3. He's been a regular since, and gets more screen time than even some of the other core members (looking at you, Josh and Jared). So he was not original core, but he is most definitly a core character at this point. If Zelena survives season 6 and continues to get the screen time she got at the end of Season 5, then I would argue that she could also be moved to "core" status.

Getting back to the topic of the discussion, There is no indication that Once will end after season 6. I even saw a user poll asking about various shows being renewed or cancelled after the 2016/2017 season, and the users that answered the poll feel that Once will be renewed for at least season 7.