Rails doesn't rely on CoffeeScript. It includes support for it by default, but you don't have to use it, and you can never start using it by passing a flag to `rails new` or removing the `coffee-rails` gem from your Gemfile.
How do the default affect the ecosystem these days, though? I remember back when I used Rails and CoffeeScript was the standard, it took a bit of work to avoid it altogether. This wasn't difficult, to be fair, but it felt like pointless busywork nonetheless.
jQuery was removed in the latest version of Rails in favor of rails-ujs, essentially a vanilla js version of jQuery so `remote: true` and things like that would still work.
Erb / vanilla js is still the default stack for beginners. But they've started to move away from the asset pipeline and they've built in webpack.
I couldn't tell you, as I haven't been really involved in Rails for a while. I never used coffeescript for any serious project, even when this change was made back in 3.1, and I can't remember it ever causing trouble. YMMV.
