Just like Product Lines and Products, Features can have a hierarchy. Since Features have a Roadmap, they also have dependencies that should be allowed. BTW, this same logic would apply to Releases and Strategy since they have Roadmaps too.
This is possible today. Through the Actions menu on each record type in Aha!, you can create a link to another record. We also recently launched an interactive dependency map which allows you to visualize the relationships across records.
You can read more about it here: http://blog.aha.io/visual-interactive-dependency-map/