Callbacks and events are significantly faster than promises, and promises I think most see as a wrapper around callbacks, with convenience functions for running and waiting on multiple concurrent async functions.

If you want promises, just embrace promisify. I get a lot of this fear about error-first callbacks being only a "convention", but everything follows this convention in practice. Anything that can't be promisified because of that will likely have a pull request or a more popular fork that can.

I don't think node core libraries should be promise-based, and you can't expect the whole ecosystem to switch to promises if node core won't. At some point you have to jump to callback-style to live on node.

I also don't really understand what this post has to do with the release.