So I downloaded the iPad OS 13 Beta 4 and tested out some of the functionality of the “Files” app that comes standard.
When I copied a file from my NAS to a newly created folder on either the iPad or within the JumpDrive attached via USB, it doesn’t allow “open-in” / direct playback within most apps you would expect (including Infuse). It will only play within the native player in the Files app, which means that it only works for limited file formats like m4v and will not give any options to .MKV files aside from copying it into the container folder of a different app (i.e. Infuse)… so you’re stuck moving around most files from the JumpDrive back onto the container folder for infuse if you’re attempting to use the native Files app in iOS13. In this regard, the Files app, even in iOS 13, is fairly hobbled unless you’re attempting to read from the USB drive a super standard file like a .mp3, .jpg, or a .m4v format (you also cannot change the file-name extensions).
The only way I see this working to avoid copying files back and forth is if there’s some API that is developed within a third party app such as infuse that allows it to directly read from what is recognized in the Files app (i.e. the JumpDrive) so that it plays directly within the app.
So I guess this is the remaining question to Infuse Devs… is there / are you planning on embedding an API that allows direct access of iOS 13 file locations, including USB locations, for direct playback?