Removing the C API function is a major breaking change. AFAIK there was no precedence since 3.0. It may be that we will name the new version 4.0 after doing this.

In any case, first than remove this API, we need to pass the following steps:

* Implement Py_DEPRECATED on Windows and use it for *all* deprecated functions.
* Get rid of using deprecated API in the core and stdlib. I'm working on this.
* I think it is good idea to implement a custom build without wchar_t cache and deprecated API for testing with third-party code. I'm working on this.

One or two versions after using Py_DEPRECATED for all deprecated functions (but not earlier than EOL of 2.7) we can make them issuing run-time warnings. One or two versions after this we can replace them with stub functions that always fail. I think they can be removed after around 5 years from now. Currently we do not have exact terms. I do not see a problem with using 4.0 as a hypothetical removal term.