Seems like DNG does behave like the RAW lite format you've just described: Everything common would be stored within the base DNG file, while everything "advanced" / more specific to a camera would be stored in additional metadata properties, which do not need to be parsed to still be able to process the base image. You can add support for these metadata on a case-by-case basis without breaking the original format, so you're not stuck re-implementing your whole raw parsing when a new camera is released as the base subset of DNG would still work.