Here is my submission to the contest, not what I originally intended but I think it ended up well...
The name of the wallpaper is Konstellation.
I was inspired by the concept of space and its relation to openness, no limits, exploration, future, innovation, technology... concepts I think KDE and Plasma represent.
Feel free to make any suggestion or comments...



Full size: https://i.postimg.cc/htQn80K3/konstellation-green.png

Released under CC By license

[[EDIT]]

I made a second version of the same wallpaper, but I like both so I'll let them as my two submissions, I hope you like them:
Konstellation2



Full size: https://i.postimg.cc/sXDFHkkK/konstellation2.png

Source file: https://drive.google.com/open?id=1eNN2wXku4EDM5JphPkTffN7lZV8JtkxH

Released under CC By license