Regarding Coffeescript and classes, I think that's a really poor reason to use it. IMO Coffeescript has had its day and if you want class sugar, just use ES6. You're already using a compilation step in your process so why not use it to work with something standard?
ES6 is pretty sweet (pun intended) and will probably make CS kinda useless in the future. I'll look into it however I think that currently CoffeeScript is a bit of a standard in the Rails world.
I just found a comment by a Rails contributor [1] which says ES6 will be supported out of the box in Rails 5, which would be ideal. I can't find anything newer to back that up though. I think it might be via ES6 support baked into sprockets.
[1] http://kryptonlabs.com/blog/2015/10/25/whats-new-in-rails-5/...