My question was inspired by Rotate fading in tikz where the inquiror is drawing laser beams that shall look somewhat blurred not as lines but as boxes with a fading. The problem with this approach is that the fading has to be turned according to the orientation via quite unhandy canvas transformations. Above that curved lines are not possible this way.
That made me think if there is way to draw fading or blurred lines in a more convenient manner, maybe by applying some kind of very closely repeated
decoration template to a path? Any ideas?