The author is preparing patches which will add support for X to the Reference Policy. However, in light of the continuing work on the supporting infrastructure and the extension of the Flask module's coverage to additional extensions, it is unlikely that the current set of object classes and permissions will remain unchanged. Policy development itself also reveals areas in which the set needs refinement.
Providing MLS support for X is an area that has not yet been seriously investigated. Because of data transfer mechanisms within the X server, notably the clipboard, an MLS desktop system will almost certainly require support within X and other desktop layers.