Node 8 and npm 5 were released last week.
Updating Node.js is probably a safe bet, but I wouldn’t rush it unless you’re really excited for its improved support for promises. It gets long term support (LTS) status in October.
I’ve been using yarn for several months and have a hard time seeing myself switching back to npm any time soon, although the latest release did add a new lockfile feature which likely came as result of the competition from yarn.