Blender devs are still able to implement their own core motion trail. I’d love if they do because my implementation isn’t the best and has it’s issues. They’d be able to make it more efficient, create more robust trail controls (mine uses Blender objects and has lots of code to compensate for this hack), and I hope they do things that are in my current list of Caveats and Limitations. I’m an animator who just happens to know how to code so I just made myself one.
As far as piggybacking, I understand the frustration. Bart Crouch’s older motion trail is the big one we all hoped would eventually get updated to 2.8x. You’re more than welcome to compare features of his and mine to see how much I could’ve copied from him. At best we only share the concept of creating a viewport motion trail. From what I understand, his implementation did not support pose bone animation and it did not actually render a world-space trail, just the local channels. These are two core things my trail offers that his does not. Correct me if I’m wrong. I’ll go check to verify these last two points.
Payment vs Free. If this was a one off thing where I upload the addon and leave without maintaining it, this addon would be free. But for as long as I’m going to publicly maintain a difficult code-base and work with people to add features everyone would like, I feel the need to be compensated. If you disagree, that’s alright.
Edit: I was wrong. Crouch’s implementation does work on pose bones and does render their world space trail, as long as the armature has an identity transform. Apologies for the misinformation.
Edit2:(Bart Crouch’s addon from August 27th 2017, can be found in Blender’s source. I just used the most recent version that wasn’t modified for 2.8x reasons. The armature has an identity transform.)
This is to show a simple case for his addon that doesn’t work for bones. Maybe it’s hindsight, but I’m curious why this was never fixed. The solution is to read the bone’s world matrix, strip off it’s local xform, and replace it with inv(stripped bone world matrix) * control world. That leads to the controls working as expected, moving with the mouse in world space.