When plotting timeseries data, it would be great to be able to add in a vertical line/boundary for a particular date. Similar to how we have a goal line, but vertical, and able to work with dates.
One use case is our lapsing users chart, which shows how many users are projected to lapse/have lapsed each week. Being able to see at a glance that to the left of the boundary, the line shows the number of people who have lapsed and to the right of the boundary, the line shows the number of people who are currently on track to lapse each week.
Another use case could be a significant event. Adding in a vertical boundary shows how the chart looked before the event and then after.