ghd, I don’t see any constitutional problem recognizing a Beis Din decision that both parties agreed to its jurisdiction, any more than civil courts recognizing any private binding arbitration (business or personal) that both parties agreed to its jurisdiction.
That’s different than creating a state law requiring an unwilling party to give a religious document, such as a Get, that they don’t want to give. The State is constitutionally prohibited from creating a law such as the latter.