The cube engine is constant development in a sense. It is in an operable state, but we are continuing to strengthen the engine.
There is already a subversion repository made up of stuff that Justice edition does not have yet, so there is a 99.9973426% chance that there will be a new official version.
Last time I checked, PlatinumArtsSandbox has not been tinkered with for some time, which makes it seem almost like an abandoned project, but who knows. I do like some aspects of that engine that the Sauerbraten engine lacks.
Chuck Norris