Although it is true that I plan to propose to use PEP 550 to reimplement decimal APIs on top of it, and so far I haven't seen any real-world examples of code that will be broken because of that. As far as I know—and I've done some research—nobody uses decimal contexts
and generators because of the associated problems. It's a chicken and egg problem.
I've been inclined to think so too. But that kind of research would be useful for decimal if—and only if—you share your methodology. It's not at all clear how one would do research to arrive at such a conclusion.
Specifically for decimal: I tried to find bug reports on bugs.python.org (found not even one), questions on stackoverflow (IIRC I didn't find anything), and used github code search and google (again, nothing directly relevant).