Most other open source software projects have adopted similar guidelines and they're thriving as well. Taking Rust as an example, they manage to put out high quality releases every six weeks. Thousands of developers of all backgrounds have contributed, which makes me think that the Code of Conduct has encouraged more participation rather than less.
There are dire warnings in this thread about how Wikipedia is going to burn to the ground because of this change. Based on experience of Go and Rust, I'm somewhat skeptical.