All (or at least those interested in replacing pywin32 in Twisted),
pywincffi is getting very close to having all the API calls necessary to replace pywin32. By my count there should be one function left, GetOverlappedResult(). All of the other functions and constants in use today should be covered and ready to start swapping into Twisted.
There's a couple of reasons I've been holding off on any integration work. First, Twisted itself has shifted development and testing workflows to public infrastructure which overall should make integration easier. The other issue right now seems to be some of the tests are not passing on AppVeyor and it's not testing across as many Python versions.
These are not big issues for pywincffi itself but I think it's probably a good idea to do the integration on top of a known stable build so we can all be confident in the results. I plan to spend some time this weekend taking a look at the build starting off by helping Craig (see thread: "Windows buildbots and Appveyor") add support for more versions of Python. After that, unless someone is already working on it, I can start to take a look at the existing test failures on Windows.
To wrap up, a big thank you to those who've reached out to help move pywincffi forward so far. Especially exvito who came up with a system to wrap cffi types, added functions, fixed some tests and contributed to several improvements on the development process.