It would be awesome to have an entry on the Epic area, let's call it 'Ungrouped', which when clicked shows all the items which are not mapped to an Epic.
Found that it is painful to scroll down the entire backlog to find the right issue, click and drag it all the way to top to drop it to the right Epic issue.

• When an item is dragged and dropped on it, it will be unassociated from any Epic it's currently connected to

Development Notes

Q: What happens to this item when there are no epics assigned to it? Will there be a way to tell it is empty without selecting it?
A: No, it does not have a count.

Q: So clicking the x on an epic link will automatically add that issue to the unlinked epic?
A: Correct (v good note)

Q: Will the unlinked epic update with the new addition in the case above if it is currently selected?
A: Yes

Q: Will this only include issues within the backlog or also issues in the work mode?
A: Epic filtering is for all issues in Plan mode so includes active sprints listed at top

Q: Does the board require a refresh in order to display these newly linked issues?
A: Uses same update as epic filtering = not a full page reload