Assume AB 849 does not directly override Prop 22. Assume both AB 849 and Prop 22 co-exist peacefully under state law and state law challenges have been exhausted. AB 849 allows intrastate SSM, and Prop 22 prohibits recognition of interstate SSM in CA.
I haven’t done the research, but my understanding of the US full faith & credit clause (FF&C) is that it is uncertain whether FF&C will force all states to recognize SSMs from other states. Generally, under FF&C, all states must recognize the official acts of all other states unless “State A” can show that the act of “State B” violates the public policy of “State A”.
As an example, let’s say CA is asked by a gay or lesbian couple to recognize a valid SSM performed in MA, an official act of MA. CA points to Prop 22 and says it doesn’t recognize interstate SSMs, so sorry to the couple. The couple sues CA under FF&C, arguing Prop 22 is unconstitutional, and CA must recognize the official acts of MA.
Under the full faith & credit clause, CA would have to recognize the MA SSM unless CA can show that recognition of the MA SSM would the violate the state public policy of CA. If CA can show recognition SSMs violates CA public policy, then CA won’t have to recognize interstate SSMs under Prop 22, and the feds can’t force CA under FF&C.
The argument is that Prop 22 will stand up as a sufficient legal barrier to an attack under the full faith & credit clause, but only if CA can show that SSMs violate CA state public policy (i.e., the “public policy exception” to the full faith & credit clause).
CA would not be able to argue convincingly that its own public policy supports Prop 22 because, even though Prop 22 is in effect, CA recognizes SSMs pursuant to AB 849.
Since CA state public policy favors SSM under AB 849, CA does not have an internal state public policy sufficient to defend Prop 22 against an attack under FF&C, and Prop 22 falls.
If Prop 22 falls under this federal FF&C attack, thanks to AB 849, then this opens the door to a new attack on AB 849 under the state constitution because AB 849 would suddenly violate the state constitution as a legislative statute that serves to void a state initiative statute.