Great article, Simon! 
Two things come to my mind which might be good to know:
→ Since you’re already using camera direction, you could add a function which pushes the whole mesh towards the camera. This way it would always be rendered in front of the sphere instead of clipping with it. I learned this neat little trick from Golembok, who used it in his campfire shader.
→ In Unity you can just scale a particle systems with a simple billboard sprite in Y direction, which results in a similar behaviour. This doesn’t work for X and Z axis nor for different orientations though (like your laser bullets).