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FYI, I've used thread-local namespaces with success in several different ways and none of them involved binding the thread-local namespace to global scope. I don't think anything needs to be fixed here.
The SO answer is misleading and perhaps even wrong. The problem it describes is about sharing the thread-local NS *between function calls*. Persisting state between function calls is not a new or mysterious problem, nor unique to thread-local namespaces. In the example they give, rather than a global they could have put it into a default arg or into a class:
def hi(threadlocal=threading.local()):
 ...
class Hi:
 threadlocal = threading.local()
 def __call__(self):
 ... # change threadlocal to self.threadlocal
hi = Hi()
This is simply a consequence of Python's normal scoping rules (should be unsurprising) and the fact that threading.local is a class (new instance per call) rather than a function (with the assumption of a singleton namespace per thread).
At most the docs could be a little more clear that threading.local() produces a new namespace each time. However, I don't think even that is necessary and suggest closing this as won't fix.