For what it's worth, this recent issue:
https://bugs.python.org/issue42762 is somewhat related to the non-async aspect of 533. (generator func getting closed during __del__ and causing odd side-effects at seemingly random points in the execution flow)
The example code provided in that issue is contrived, and involves catching unconditional exceptions and recursing, but following the code flow in that situation feels unreasonably hard, and deciding if it's a python bug or not is even harder.
I'm not sure how easy an implementation of 533 would be that doesn't break a lot of existing code, but if one could be made, it might help make generator lifecycles more predictable.