The brief in the Proposition 8 litigation filed by Jerry Brown, the state's Attorney General, agrees with the petitioners challenging Prop 8 that the measure is a more profound revision to the Constitution, not a minor amendment, and therefore unconstitutional because it cannot be adopted through the initiative process that was used.  While this does not guarantee that a majority of the California Supreme Court Justices will agree, it is a big development in the case and likely to weigh heavily in the Justices' minds.

UPDATE: Actually, the Attorney General's argument is that, although the challengers have not to his mind shown that Prop 8 counts as a revision, Prop 8 is nonetheless invalid because it attempts to eliminate fundamental rights without a compelling justification, which in his view is not a power encompassed by the initiative-amendment power.  So, although he doesn't agree with the revision argument, Jerry Brown agrees with the challengers that Prop 8 is not within the initiative power.  Interesting nuance, perhaps offering one or more Justices a third path, one that doesn't accept the revision argument but that nonetheless holds Prop 8 to be invalid.