I often have users ask me how I would display a level of certainty around a particular milestone or task.
The need exists because the initiative spans many years, and therefore, items in the plan set to begin, or complete, in the near future are fairly certain in terms of their target dates. However, items further out on the timeline need to be interpreted as loose estimates.
This is actually very easily accomplished in OnePager, as long as you have a column with a value that indicates the various levels of certainty you want to communicate.