... Currently, it is necessary to specifically test whether a node is an instance of `str` and stop drilling down in that case. One could say that's a minor issue, but it's a minor issue that affects a lot of development efforts and has do be worked around separately by each developer who encounters it. ...
Can you show us before and after code so we can gauge how or if this improves things?
I'm a bit skeptical that it does anything other than replace an instance check with a different check.
In Java, one of the annoyances (to me) is that strings aren't iterable or subscriptable. I would fix that if I could, which is the opposite of what you propose for Python.
--- Bruce