Best for low res mockups in my opinion is (and will for ever be) pencil and paper! And as for high res mockups, if you're a Mac user, Sketch is a really powerful prototyping tool that is pretty easy to learn.

Since most client-side interactions, libraries and frameworks are JavaScript based and the basics of Node.js are so extremely easy to get, it seems lazy not to care about learning a couple of things about it. As I take it, the more understanding there is between the back-end devs and the front-end devs, the easier will be the streamlining of their development processes. And that not taking into account that most tooling utilities is built around Node, as others have extensively and correctly covered.

True but, as @jiyinyiyong says, if contributors can keep the relevant features onto it it may be worth it, I'm not a fan for brackets and the syntax they use is nice.