I just don't see Iran getting the FC-31.
1. Pakistan and Saudi are both Sunni countries with a long-standing relationship where part of the Pakistan military works for Saudi Arabia, and where Saudi provides funds to Pakistan. Saudi and UAE are also close allies in most respects.
2. Saudi, UAE and Pakistan all see China as a superpower which will one day eclipse the US in economic power, as per the surveys. Given time, that economic power will translate in military power.
3. China is Pakistan's most vital strategic partner in its rivalry with India
4. China is also the most important customer for the oil and gas produced by Saudi. Presumably this applies to UAE as well, but the numbers aren't readily available.
5. China is also the most important import partner for Saudi and UAE
6. Iran has nowhere near the financial clout of Saudi Arabia, nor the aerospace production capability of Pakistan.
7. Saudi and Iran have tense relations, and Saudi doesn't want China to turn to Iran. A FC-31 project involving Saudi and China would lock in a strategic partnership, probably involving Pakistan and UAE as well.
8. UAE has suspended a contract for 50 F-35s, so is weighing its options.
EDIT
9. China is at the forefront of solar and battery technology. Saudi is one of the best locations for solar as it has lots of desert and sun. Note that Saudi currently burns a lot of oil to produce electricity. But it's cheaper to generate cheap solar electricity (now at 1cent/KWh in Saudi) and sell that oil instead for a lot more money. Saudi and China both know that oil demand is going to decline in the long-term.
Don't forget that China also signed a huge 25 years cooperation program with Iran. Iran is soon full member in SCO. That is something SA has not committed to China. Why would China upset someone who is already a close partner for a "potential" one who is still flirting around?
Importantly, religious sect playing absolutely no role in China's diplomacy.
Also note, just like Turkey and Greece in NATO, Turkey was buying F-35 just like Greece is doing. If US has no problem with it, why would China allow herself to be "blackmailed" by a potential future "ally" against another? Superpower doesn't allow it.
China sold weapons to both Iran and Iraq during their war and non of them could do anything or did anything about it. Why can't China do it again? China established diplomatic relation with SK against the protest from NK. Why bother now?
It is SA being locked with China if they choose FC-31, China is not locked nor would China allows herself being locked to any regional power against another one. A lesson learnt from the history.
About SA's leverage, remember that the SA and China's approachment is not single sided that China need SA, but SA need China as well. The game plays in many ways. Let's say China sells FC-31 to Iran, what is SA going to do? Turn to US for F-35? That will give US the leverage over SA like "hey, now you beg me for F-35, how about you cutting off everything from China?"
