Ken Case, writer for The Omni Group:
In 2019, we think it's time to pull our custom document reader to the advantage of using Apple's built-in document reader – and with our iOS 13 updates this fall, we're going to do just that the. Instead of viewing our custom file browser, you will be presented with the standard iOS document reader – just like in Apple's own iWork apps. Using Apple's browser, you will be able to store and sync your documents using Apple's built-in iCloud Drive, or third-party commercial options like Box – or even in cloud or self-hosted git repositories with Working Copy.  Syncing through OmniPresence will still be an option, but it will no longer be the only integrated option. In fact, it may be the least privileged option: Since OmniPresence is not its own separate app, it is not listed in the document reader sidebar where you will find other document storage solutions. Instead, it will present itself on iOS much like on a Mac ̵1; like a folder of synced documents. We're not trying to remove people from using OmniPresence – but in 2019 we don't think it makes sense to push people against it either. OmniPresence is not a core part of our apps or business, and in 2019 there are many good alternatives. Seamless document synchronization is important for our apps – but where and how these documents are synchronized is not!
This is an excellent change and I hope more apps are moving towards. The Document Browser in iOS is really a special view of the Files app that is used as the root file management interface in document-based apps that use it. As Case points out, all Apple iWork apps support the document reader, and several important third-party apps do as well, such as PDF Viewer, MindNode and Pretext. The document reader not only allows users to store an app's files in any file provider they want, but the other primary benefit is to provide a unified file search device for users on iOS. As more apps use the document reader, the unified experience becomes a reality for iPad and iPhone users.
The timing of the Omni Group implementing the document reader is not surprising: this fall, the Apple Files app will be updated with support for external storage devices such as USB drives, a new column view, shared iCloud Drive folders and more. By using the document reader in apps like OmniOutliner and OmniGraffle, the Omni group gets the benefit of having all these new Files features built right into their apps.