It seems to me that Node should ship promisify-ed versions of all these functions (e.g. fs.readFileAsync). Over time they could replace the implementation with ones that use the OS Async APIs, though perhaps this step is unnecessary if you're already using an event loop underneath.
I mean, they've been debating about how to add a promisified API for years (see for example https://github.com/nodejs/node/pull/5020) but nothing has come of it. util.promisify is a welcome addition, but very late for a first step.
[0]: https://medium.com/@styfle/promises-in-node-js-8-x-core-d6a8...