CDDL 2.0 and beyond -- a draft plan

The Concise Data Definition Language (CDDL) today is defined by RFC 8610, RFC 9165, RFC 9682, and RFC 9741). RFC 9165 and the latter (as well as some more application specific specifications such as RFC 9090) have used the extension point provided in RFC 8610, the control operator. As CDDL is used in larger projects, feature requirements become known that cannot be easily mapped into this single extension point. Hence, there is a need for evolution of the base CDDL specification itself. The present document provides a roadmap towards a "CDDL 2.0"; it is intended to serve as a basis for implementations that evolve with the concept of CDDL 2.0. It is based on draft-bormann-cbor-cddl-freezer, but is more selective in what potential features it takes up and more detailed in their discussion. This document is intended to evolve over time; it might spawn specific documents and then retire, or it might eventually be published as a roadmap document.