I think it would be a good idea to include 'release to release' dependencies across product lines. The portfolio view is a really good view for high level and progress but i think it would be great to show high level dependencies from a release, to another release (in another product line) in order to model cross-productline relationships.
Thanks - James
This can be achieved through the Release page, as well as the report page. We offer the ability to create and report on release and feature dependencies across products.
Please see this blog post for more details: http://blog.aha.io/index.php/just-launched-easily-visualize-and-report-on-roadmap-dependencies/