I agree with you except that I would think the people changing the state constitution would trump the CA Supreme Court. The decision on what the people can do within a state would then be decided at the next higher level, which would be a federal district court, to ensure that the people of California did not in some way violate the Federal Constitution (and I don’t think they did).
However, I believe that the US Supreme Court will try to thread this needle along the lines of what McConnell wrote. Something narrow, not broad.
Allowing SSM in California, overturning not just a hotly debated statewide referendum, but also a CA SSC ruling isn’t narrow.
I’m not convinced that democracy is the best way to sort out rights. That the CA SSC affirmed Prop. 8 goes a long way toward telling me that the process was legitimate and that homosexual rights are being retaind in other, acceptable ways in CA. It isn’t like CA is a known hotbed of conservatism. Plenty of pro-SSM money and PR were poured into that campaign. The time to overturn it was at the state supreme court, not SCOTUS.