The difference between a Motionlight and a Arealight is, that if you want create a LightSub-Path, starting from this lightsource, than you have to create first the point on the lightsource and than you must move that created point randomly on a given Line (the motionline from the lightsource).
Or if there is a EyePoint, from a Eyesubpath, is given, and you want connect that eyepoint with a random point on that lightsource, than you create first with lightsource-sampling a point on the lightsource and move it randomly to get to motioneffect. Its not as diffifucult but have to be done for a nice looking fireball
PS: If you look on the last image, there are other details: Microfacet Glas on the brown mushroom and Microfacet Metal on the turtle. Bummap-effect on the tetris-stones. This effects are so small, no one can see that
I will post in some days a better image from my microfacet-testimageszene.