Since we're looking to diffuse and even out the pixels, some of the designs wouldn't work as well. I think a swing triggered persistence of image effect could be possible to some extent. Your flaming sword idea in particular could be plausible in theory.
There are definitely folks that have more knowledge and experience with this, but I've been thinking about what I can do with my neopixels. This concept, in the broader sense, has definitely crossed my mind.