Leo M commented
Interactive states of an element would allow small changes like on/off button, expand-collapse menu to achieve without repeating an art board, thus getting into messy to navigate art-board system
David Knell commented
It would make sense (to me, anyway) to have this be a control in the inspector (probably in prototype mode, right?). You click on an element and, just as you can add multiple shadows, you can add a cursor state: which cursor (from a dropdown) and when it appears (from a dropdown: hover, click, downpress, etc.). I suppose the artboard would need to have this option in its inspector as well.
Come to think of it, when you add a link to an element, the default should be that the cursor changes to the hand cursor when hovering over that element (for desktop interfaces, anyway). It's really helpful to see the hand cursor in a prototype so the user can know that they can click something, as they would be able to do in the production version of the app.