For iPadOS 14, in addition to what other people said:
- Time Machine =)
- Ability to set a default "Open With" for different file types (kinda related to default apps but not exactly the same).
- Resizable UI panels to better use space (The sidebar of the Files App is huge on my 13 iPad Pro).
- Universal Command + N shortcut to open new windows. At the moment, you need to go to App Expose and tap the "+" icon (why don't we have this already? It drives me crazy when I think about it! ? ).
- Universal Command + X shortcut to close the current windows when multiple windows of the same app are open. Perhaps, after closing it, send the user to the most recent still-open window from the same app.
- Option to start split screen multitasking by dropping windows into each others from the app switcher (this is another feature whose absence I cannot explain. It would make multitasking so much easier. And by the way, this is exactly how it works for fullscreen windows on a Mac).
- Ability to add own music files to the Music App and/or better music player integrated into Files.
- Bonus little thing: ability to set icon size in the Files App (or make them smaller on the 13", ATM they are huge).