Thanks Atlassian for adding backlog to kanban boards, this is really helpful, but I think it shouldn't be based on status, as this will complicates the workflow and make it hard to switch from kanban to scrum back and forth,
I suggest to make just a flag, as you throw any ticket to the the backlog regardless of the ticket status, similar to scrum sprints,
This will help in planning and flexible in managing backlog items
https://support.atlassian.com/jira-software-cloud/docs/use-your-kanban-backlog/
