Yes with hindsight I wish I had written it in JS, but writing the BS compiler was something I wanted to get done fast, and I'm more proficient with Ruby.
BS has the #x{foo} syntax for htmlEncoding, or did you mean that should just be the default?
I don't mean to come across as an ass, just curious. Though, I do think what you are doing could be a natural extension to CoffeeScript itself.
Also, I would suggest having an htmlEncode(variable) by default, I know that htmlEncode isn't a built-in JS method, but you should want to escape html entities.