Neat Peter! Would there be any issue using the rayProject node when you need the camera's perspective?
I saw this question yesterday and tried another way of going about it. Starting with a scatter node culled by camera, then pointCloudToMesh into a timeOffset-1 to return the points from last frame, then into a bounding object>group(inverted)>PATA to return only the new points created on the current frame. Then a Python procedure called in a Maya expression that on frame 1 gets the initial scatter points, and every frame after, adds the new points to the array. And then sets a PCTC with that array, so the curve grows as the camera moves. Probably easier ways of doing it, but it does seem to work.