Well. I do use Vanilla-JS quite a lot. Also I do not think that it's a
full circle back
since people never really left Vanilla-JS. Well, at least people who know how to JS never really did. But as always, it ultimately depends on what you are doing. On the one hand, if you are working on your personal site with a portfolio, there is no need for any library. It's just Vanilla-JS. On the other hand, if you want to build a Facebook, you might want to use some lib to make your life easier.
You see, I am no fan of React, and I do not really like Angular. Both feel like tattooing an ant; with a low orbit ion cannon. I like Polymer, or rather web components. So all I need is a shim until we get stuff into our browsers. The rest is Vanilla with whatever pattern I think fits best.