Lars and Dan,
I understand that it might be out of scope for this release, but I would like to suggest that you look into the XML dialect for scalable vector graphics (SVG) as an output format for workflow renderings. If graphviz-like libraries exist to that assist in the creation of SVG directed graphs (I'm not sure about this), it would be very cool to have the option to publish either interactive/plugin-enabled versions of the workflow , with zoom, pan, expand/collapse etc. or a static jpg rendering with a server-side SVG->JPG conversion library (which does exists, AFAIK).
Also, if you want an example of a workflow that could have benefited from hierarchy and did use parallel routing, you can check out my incomplete peer-review module writeup:
http://www.pobox.com/~johnseq/projects/peerreview/wfnotes.html
