Idea suggestion 1: Shape detection. Presumably this is already present given that it looks for the borders of the viewscreen. It would be really great if it could detect potential buttons in the app, and auto-select them to improve the speed of the workflow.

Idea Suggestion 2: Color coding. Use a highlighter to color in buttons in some color. Your app would automatically recognize things of that color as buttons, and potentially erase the color in the "finished" prototypes.