Where it gets interesting is when China comes out on Iran's side.
That's not even remotely possible in my humble opinion. For one, they're too far to send any kind of reinforcements to Iran. They cannot challenge us on the seas, and, further more, they could not even mount a feasible Taiwan invasion at this time. It's a complete lose-lose for them to join in on Tehran's side. And that's if they could keep the lid on their own internal unrest.