A nice feature would be some simple shape object, with options for lines, circles, rectangles, and simple color control. This would come immensely in handy with simple emitters such as gunshot hits, blood, and other simple particle effects. Random colors could be utilized for a nicer looking effect and for more in-depth customization. And lines, well, having two X and Y coordinates would make life a LOT easier.
I hope you can add these to your long list of features planned for the amazing engine that is Construct 2.