It says it doesn’t support OmniFocus 2 and “Dropping individual actions and Inbox items” is the new feature. Could you not drop actions in the inbox before? Is that what needed a forced upgrade to the new database that wasn’t backward compatible?
You couldn’t drop actions before at all—only projects. Now you can decide not to do an action and the database can represent that, instead of a workaround like deleting or completing the task.
The database has been restructured and will facilitate future features that will be coming. You won’t see anything now besides the dropped status. But changes are coming.
I think another feature that is not available in the older OF2 database structure is having multiple notifications for tasks and projects.
I can guess that task sharing will be a feature that will require the new database structure.