You can already create polygon PCB outlines in the pattern editor - but you don't have access to tools like the radiused corners.
(Nor can you copy a PCB outline created in PCB Layout - to store it as a pattern to use in future designs)
Having a library of board outlines would be useful to many people - particularly DipTrace provided outlines for things like Arduino boards etc.
Create complex PCB outlines in the Pattern Editor
Re: Create complex PCB outlines in the Pattern Editor
You can convert a board outline to board cutout shape in PCB Layout. If you select the shape with one or more pads or mounting holes, then right click on any of selected, convert them to a component. Further, right click to the component and save it to either active or new library.