This is mostly a concern for knowing “where did they go”?
If not all features are added to the Releases -> Roadmap view, it would be nice to have an indicator, both on the Releases -> Roadmap view and the Features -> Details view to indicate whether a feature is visible.
On the Releases -> Roadmap view, Maybe instead of “add existing features”, it is something like, “include existing features (#)” and the number shows me how many there are to still add, or hide that option when all have been added.
Similarly, on the Features -> Details view, there could be a checkbox for “include in release roadmap view”.