Are you saying the current JS loops will stop working at that point? Of course not. So why would it matter? CoffeeScript -> Javascript will continue to work like it always did.
current js loops for sure will not, but I guess maintaining full backward compatibility would be a hard task, so I assume at some point CS will evolve to support only the newer standards. ie6 compatibility it's something jeremy talks about in the podcast I linked in the other comment here.
