Milestone Status
Sometimes a Milestone is just a date to be aware of, with nothing actually to start or complete. It would be nice for them to either not a have a status (like new / completed) or have a status that doesn't require an update (like Deadline).
This category could also be helpful when items like an event that are over a range of days and doesn't qualify as a Milestone, but you'd still like to see in relation to all of the tasks.
It would also be nice if you could have it be a duration of 0. The definition of a Milestone according to PMI is just that: zero duration that shows an important achievement in a project. Not sure why the date does not move either. If you are using dependencies and something in the path impacts that milestone, you would want to be able to immediately identify that with a change of date. Then you can either notify stakeholders or ensure the predecessor tasks don't overrun original plan.