Be able to resize multiple items at once — e.g. containers containing child elements. Reuse the existing Scale functionality, but implement it as part of the UI tools for ProtoPie UI itself, rather than an action that needs to be triggered. (Similar to how Sketch, InDesign, etc. have scale tools to resize objects.)
This would be extremely useful for containers that contain multiple child elements (other containers, shapes, text fields, etc.) because currently the container and each of its child elements need to be resized separately.