Okay. We (Ned Deily + Steve Dower + me) talked it over here at the core dev sprints, and they convinced me that it's basically okay to add the CHACHA20 string to 3.4 and 3.5--it has some history, and OpenSSL is a little different, etc etc. So go for it.
I suspect it won't affect very many people anyway, because not many will use Python 3.4 with a version of OpenSSL that supports ChaCha20. It's more likely with 3.5 users--not with our binary installers, but perhaps the Linux distributions that release during what remains of 2016.