add the optional ability to post backlog in a column on the visible board view
On a physical kanban board, you can have an area to "display" the backlog along with the WIP which gives upstream and downstream stakeholders the ability to look into your backlog and see what you (or the operational review board) did not select for prioritizing. This is very often useful when not everyone who has a stake in your work can attend every prioritization meeting and you have a relatively high velocity and variable WIP flow.
Bors Vesterby commented
This is critical for Lean project work where the goal is to visualize all work including intake into your backlog. Hiding the backlog, frankly, goes against a fundamental tenant of Kanban which is to make ALL work visible.