In the same way that you are able to compute capacity estimates for teams on an initiative by features and master features, it would be helpful to compute from child initiatives.
This would allow you to roll up team based forecasting up the hierarchy.
A program manager is managing a large program as an initaitive at the top level of the hierarchy
The program is split into multiple projects across business units (which are product lines in Aha!) which are further broken down into the different workspaces
Estimates are captured by each project manager for those projects for their various teams
The program manager needs to roll up these estimates and report on them from the highest level.