Something that I'm not particularly fond of the widget popups are the check boxes. In earlier versions of plasma they were huge, now they're smaller and more appropriately looking but I can't help but feel they add clutter in a way.
What do you think of a possibility of them being toggle buttons (so they can be pressed down when active) or to have some sort of active indicator.

Below is something I quickly made in KolourPaint to demonstrate what I'm thinking about. You can also vizualize them as pressed buttons. My paint skills are not sufficient for that one.