Given that Plasma Active only released officially a little over a month ago, I'm sure there are more than a handful of improvements to be made yet. But they are designing for smaller devices.. tablets, phones, set-top boxes, etc., so they're working toward a minimal footprint. Though I'm also biased toward KDE (and heavily Qt biased), being a very long-time user on the desktop. Their technology that they're building on, Plasma, is incredibly powerful and useful. They do more than just make some random interface, they study the whole user interaction process and develop the experience around what they learn.
There are a few nice demos on youtube with Plasma Active running on tablets, definitely worth checking out.
Sorry if this sounded like a KDE PR speech