I think I managed to create a generic and versatile setup for lightsaber rotoscoping and applying the actual effect. I created a Nodegroup where you can just feed in the image of the lightsaber and the desired color.
I experimeted a lot with the best techniques for the actual rotoscoping work. But I always arived at the same conclusion: to really get satisfying results you have to rotoscope each frame.
Here is a still with a crab sith lord sitting on my staircase
The original footage from the video below was taken during a hiking trip not far fro were I live. My daughter and her friend is acting as jedi padawans in a rather dramatic environment. Pity was they just had wodden sticks as lightsabers, which was a really tedious work to rotosopce correctly. Any way this is my first attempt. I will improve the flashes ro be more dynamic. A completely new area will be the sound fx, which I will add later on.
I will submit these entries to the actual lightsaber rotoscoping challenge at blenderartists, and after that I will upload the blend files and a description on how to use the lightsaber node setup.