I'm pretty sure CHAOS just gets used because all the names in class IN have potential meaning to other systems --- you can't just make up random IN names, because you could be screwing up someone else's domain (unless you tediously nest your made-up names under your own domain). But there's no risk of that with CHAOS, so it's a free-for-all for random DNS features.

You'd use a new class, like "RANDOM" or something, except that no deployed DNS software knows about that class.