[boomlinde]

I'm not categorically against deprecation warnings. Isn't gunicorn a command line tool? I can respect such warnings in a tool or even sometimes a library, but not in a language interpreter. The user should as closely as possible be in full control of the streams in those cases, and any standard error output that isn't an exception (i.e. either deliberate or resulting from a programmer error) should stay the hell off.

The proper way to handle this is of course to introduce a new semver major version. No need for deprecation warnings because incompatibility is expected.