Many iOS apps auto-enter an “edit” mode when the keyboard is active (i.e. when you tap in the text field and enter a “preview” mode when the keyboard is dismissed. Evernote is a good example of this.
This would be an amazing feature for Obsidian. Of course, the current preview/edit button would still exist; it would just toggle this mode on and off.
Live Preview does not remedy this issue, though it ameliorates it somewhat. I would still like this feature, except that it would switch between Live Preview and Reading mode.