Uncertainty in Product Backlog is a big risk for the project schedule. The problem is that the full scope of the release can be quite hard to estimate because the requirements are not well-know early on. Confounding this problem is that frequently the release date is a hard deadline. This means that a team must perform an unknown about of work in a fixed amount of time. The “Cone of Uncertainty” describes the reduction of the uncertainty about scope after each iteration. At the uncertainty is eliminated and the exact amount of scope is known.
In anticipation of scope problems, the development schedule should be aligned to address the highest priority feature sets and features in early iterations, and defer lower priority feature sets and features to later iterations. To reduce risk around missing a release deadline further, the Requirements Lead should activity defer low priority features from all feature sets to later iterations. This avoids the case of being unable to release a minimally acceptable product because time was spent on low priority features from high priority feature sets when it could have been spent on all individually high priority features across feature sets.