Ability to add a horizontal reference line for a particular date on Timeline view

Hi there,
I love the Timeline View which clearly gives a visual reference.
It would be great if we are able to add a horizontal reference line (or a zone, or lines) for a particular date, say, the product launch date.

Perhaps it could be the ability to mark a pulse’s start/end/or both dates a horizontal line across the Timeline view.

It will help a lot.