Calendar should be updated to use EditEngine. Among other things, this would give us better and more flexible behavior for the "Create Private Event" / "Create Public Event" dropdown: installs could customize the forms and choose their own defaults.
T10673 is a similar task with some pointers.
New Calendar events should have Public visibility by default ... or a setting should allow admins to define which is the default. Currently is All Users, which is inconsistent with the default for Tasks and other defaults.
Original report: https://phabricator.wikimedia.org/T110503