write on effect can do this as a stroke. and you could use a painted texture as a matte so it looks like its being painted on.
Besides having no idea what you're trying to say, I don't think you're considering the problem.
Here's the same issue, solved with regards lines and their strokes distorting:
That's a particularly cool trick.
But I don't see anything similarly possible with Paint Brush based "strokes".
Please, consider that this is what I'm "painting" the line with, so I'd like the circles (dots) to not distort into ovals when scaling the path in only one dimension, see my answer at bottom:
I'd use a mask on a solid for this. Double-click on the mask to activate the Free Transform tool. Scale it just horizontally, just vertically, in both dimensions or rotate it if you so choose. You scale the path without scaling the stroke you want.
Can a "mask" be a line that's not a closed shape?
Also just found out that paths can be whip picked, so can be an instance of a master path somewhere in the project.
Clumsy how it's done. But it seems to provide "reference" style delineation.
I think I'm beginning to see the extent of the limitations of the AE approach to "vectors".
It's not a logical approach to treating vectors as first class citizens of the AE environment and paradigm. They were included as an "add on" feature, without due consideration to how they might be best used.
As such, they live in a space between worlds. Not of themselves in the traditional sense of a Spline, and not of the AE system and approach because they don't make a natural fit into a pixel based compositing world that's not made the full transition to Spline based nodes/vertices and their editing.
As a result, Shapes and Paths and Masks are incredibly INEXACT things, without the normal granular controls one might expect from such things... in just about any other app.