The best way to share Omnifocus projects is probably by exporting and importing Omnioutliner Professional files (although importing the Flagged and Completion Date fields is not yet supported in OF ver 71)

Text files, however, also have their appeal - they can migrate across platforms, and be read and generated by by colleagues who are not using Omnioutliner. The TaskPaper format works quite well for this purpose, and can be read and edited with or without the Taskpaper program.

I have drafted extensions of my Taskpaper import and export scripts for Omnifocus, aiming to make them read and write start and due dates, flagged status and estimated minutes, (in addition to the default context and @done tags).

The tags which they aim to read and write have the following formats:

@start(yyyy-mm-dd) or @start(yyyy-mm-dd hh:mm) - Start date
@due(yyyy-mm-dd) or @due(yyyy-mm-dd hh:mm) - Due date
@mins(nn) - Estimated minutes
@flag - Flagged