Serhiy,
I like the idea, but in typeshed we have an agreement to always show a default value by an ellipsis.
For example, definition like this:
def fun(x, y, z=0):
return x + y + z
can be represented like this
fun(x, y, z=...)
or if one has annotations in the definition, then
fun(x: int, y: int, z: int = ...) -> int
So if you would make this change, I would prefer the existing "style".