A possibly needless clarification: The DNS is organised by class, name, and then type. Each class is a seperate space, so ycombinator.com in the IN (Internet) class and ycombinator.com in any other class aren't necessarily the same entities. Types can also be class specific, for example A in the IN class is different to A in the CHAOS class. Types may also only be defined in specific classes like SRV (amongst others) in IN. (Aside: this model is why CNAMEs can't coexist with other records.)
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.
