The Roadmap Portfolio view is the clearest way to visualize "things over spans of time" - the Roadmap Timeline view seems to be more for "visualize things at points in time (releases)".
The Roadmap Portfolion view would have additional clarity if it was possible to view initiatives as groupings over features as they are laid out over time (answering: what are the time spans spent on this initiative?). Goals could also be usefully visualized as points when attached to initiatives, releases, and features.
We recently launched Report Timelines which allow you to create Timeline views around anything in Aha! which has a date tied to it. There is a wide variety of customization which can be done here. We've created a few example reports, one of which is a Timeline view of Initiatives by product and goal.
Our Strategy roadmap (based on Initiatives) is also another way to visualize time spans spent on initiatives over time.
Because of these additional capabilities, we are unlikely to make updates to the Release portfolio view at this time but we will keep this idea open as we continue to get more feedback.