NoCaseMatchError (or any other name) which is a subtype of IncompatibleClassChangeError.
I buy the "subtype of ICCE" argument, but it seems to me these need to be exceptions, not errors. (Thought experiment: if we already had both ICC{Exception,Error}, would we have jumped so fast to Error? I don't think so.) I'd support adding ICEException and having these be subtypes.
Adding a new enum value is not the same sort of obviously-incompatible change as changing a static method to instance, or a concrete method to abstract, which are the sorts of things that trigger ICCError.
On the naming front, I would think this is more in the category of "unexpected class change exception" than "incompatible change." Adding a new enum constant isn't intrinsically evil. If anything, the issue is on the client, who relied on the assumption of of exhaustiveness.
