Based on my previous mail "Manual Ordering and Dynamic Priority" I would like also to comment about this related idea.
In Agenda, it is possible to generate different views. I wonder whether it would be possible to generate an "org mode" view. That is, a buffer in org-mode format with all the tasks from our agenda query (no really a sparse tree view). Then that file could be edited and reordered to create a planning. If the file could also sync with new queries that would be great. I think of that maybe as a package called 'org-projection' (project org into org). With such feature, I could have a general org file e.g. for a working project, and then a planning (projected) file in association with it. I would add the latter to the Agenda files. I can't do lisp development and have no idea if that makes sense, but I just wanted to share this idea with you.