live drawing with reverse function —> fading line

When you say 'Live' does this have happen to a line as you create it?  I mean as opposed to an animation of a line appearing to be created, and at a given time, the start of the line would disappear?  If you think about it, this would look like a length of cord was being pulled by the brush?  It would be rather like a very long brush smoothing leash.

What sort of background would there be?  If it was plain white, for instance, you could animate the line being drawn in black.  Then copy the video layer and invert it (to white, and move it on the time line according to the required delay.  The second layer would draw a white line over the back effectively making it appear to fade.  

I think this is going to come down to the details of how it needs to work, and what you mean by live performance?  You could always use magic.

I am afraid Photoshop itself at least won’t be »it« and I am not sure any Adobe application would fit the requirement. 
Have you asked over on the Adobe Fresco Forum? 

Have you seen any videos that show what you want to achieve done by someone else live? 

On the one hand the process sounds like something fairly straightforward, on the other hand it sounds like something fairly »niche« … 

The live-performance-aspect just doesn’t seem to chime with what most Adobe applications I am familiar with are targeted at.