Maybe this is just wishful thinking from someone who grew up in front of a physical keyboard, but I sometimes wish that my phone had a global "undo" button.
I'm sure there's a reason why phones have evolved away from having such a feature, but sometimes, especially when editing text, it would be very useful to "just hit ctrl-z", or whatever it would be on a phone. Some apps do have such a button, but they explicitly had to place it there and craft a feature around it.
I can imagine that Android and other OSes are capable of exposing an "undo" API that apps can implement to make this easier. A gesture well known to the user, similar to the "back" button or gesture on Android, would trigger an undo. For text, apps probably won't even have to implement anything. The Textbox element of the UI framework should be capable of undoing changes. For anything more complex, the app decides what to do with this action.
Again, probably just wishful thinking, but I really want my undos back!
This is post 078 of #100DaysToOffload.