If I understood correctly, they would become keywords, like 'return', 'true', 'false' are in javascript, and 'class' is in coffeescript. The problem with it is that any functions called defer would have to be renamed in order to work on this version of Coffeescript, possibly breaking some existing code.
This is really pedantic, but I also think it's important: class is a keyword (well, really just a reserved word) in JavaScript as well. The reason it's important is that some engines will actually have issues if you use syntax like this[1]:
Yeah, we are kinda splitting hairs here, but strictly speaking, 'class' is reserved word in JS. It will become a keywords when they start using it. The link you provided does make this distinction: reserved as future keywords.
