It is interesting that protests in Karachi are larger than some Islamic countries. I interact with many foreign students here at the University, the Pakistani students tell me that Pakistanis try to be more Arab than the Arabs themselves, and Iranian students make it a point to remind me they are NOT Arab and have their own language and are proud of it! Saudi and US of course as you know are bedfellows of convenience. It's been that way for years and years, something I don't quite approve of.
I don't think there will be an open confrontation either. Yes, the US killed the second most powerful man in Iran, but he was overconfident that no one would touch him and was pretty open about where he was. So he painted a big target on his back. The US saw the opportunity and took it, also killing a high ranking Hezbollah target I believe.
Iran will have to make a response, but one that does not unleash the full fury of the US Armed forces. Asymmetrical response if you will