I don't quite follow this request; can you elaborate?
If what you're asking for is a way to do a "line draw" animation on an entire shape, which may look like a line, then I think the way a future version would support this is via masking with a shape layer masking your draw shape.
There's the possibility of this, and to some degree you can do it now via SVG filters. Please see @MaxZieb's work in this thread:
As with your above question, the bigger point is that those paths aren't really paths, they have become full shapes. I imagine for a variety of needs we will need to have the ability to turn paths into their shape outlines for a future release.
Thanks for the feedback!