Fedakius, thanks for posting your request! I figured I could implement rectangles pretty quickly, so here you go. It screwed up my presentation a bit, my 'add shape' buttons aren't all on one line any more, but I planned on redoing them anyway.
Next I plan on working Backbone.js into the code. It won't offer any new features on the surface, but it will allow me to implement new features more quickly. Then it's on to saving and sharing plans.