[Ken Case]

Make a copy of your OmniFocus database and open it, and you'll find that OmniFocus already supports multiple documents. You can open multiple windows on each, make edits, drag between them, and so on.

However, there are some features of OmniFocus that only work with the primary document: Quick Entry, Syncing, and Perspectives are the things that come to mind off-hand. (Each of those features needs the continuity of always working with the same document.)