While the use case makes sense, test if an application relies on the dictionary iterating order, I'm not sure that adding an option to change the order.

For me, it's a rare and very specific use case, whereas your option is public and "too easy" to find and use. For example, what if a developer decides that its application now requires this option to run?

Moreover, your code changes performance critical code. I don't want to get a slowdown here for rare use case, since we spent a lot of time to optimize these functions!

I suggest you to try to implement your feature in a dict subtype in a third party module, and try to monkey-patch applications to use your type. Attached hack_dict.py is an example, but it only handles code explicitly calling the "dict()" type to create a dictionray.

Another option for you is to maintain your downstream CPython patch, sorry.