This idea has been merged into another idea. To comment or vote on this idea, please visit APP-I-1366 User Story Mapping.
To really find out what's important in which granularity, we use UserStoryMapping with e.g. storiesonboard.com or feature map.co to determine which feature of an epic/featureset shall be delivered in which release in a lean way.
it would be really awesome and a great experience to have this directly in aha.io, so you'd never have to leave the best tool on earth for agile roadmapping when you're in the creative process :)