It’s all in the title. It would be very nice to be able to move items across columns with a keyboard shortcut.
I can understand that the shortcut might be confusing for some users (a bit like Cmd-Shift-9 and Cmd-Shift-0 can be), so maybe it would be useful to just define move_to_next_parent and move_to_prev_parent, and allow users to define custom shortcuts for it.
(By the way, custom shortcuts are so wonderful, thank you, thank you, thank you 
)