> ssl.SSLWantReadError and ssl.SSLWantWriteError should inherit io.BlockingIOError.
> Generic code that works with non-blocking sockets will stop working with SSLSockets.

I'll have to think about that, but in any case non-blocking SSL code needs to be subtler than normal non-blocking code, because of this:

> Does anybody have any idea if SSLSocket.read() will need to write to the underlying socket or SSLSocket.write() need to read from it? AFAIK they don't.

Yet the documentation clearly tells you they can:
https://docs.python.org/3/library/ssl.html#notes-on-non-blocking-sockets