We have added two new functions under Special > Display Functions in the Hotkey Editor (Preferences > Interface > Hotkeys/Menu Editor). These functions allow you to define hotkeys to toggle between your stages.
Toggle Stage lets you cycle through all your stages, making each stage the working stage in turn.
Toggle Stage Exclusive makes each stage the working stage in turn, and sets the Window Source and Background Source to match that stage. It also makes all other stages invisible. The visual effect is equivalent to having a single stage present.