Like I said previously, KSA and Pakistan concerns play key role in potential China-Iran arms deal that's why the chance of which is next to zero.
In my view, China will be mistaken to assume that it can gradually detach the Saudi regime from its American patrons by inking major economic deals with Ryadh and by supplying them with nuclear technology and strategic types of weaponry (in particular BM's). Likewise, Beijing would miscalculate by postulating that in case of a major conflagration between China and the US, Ryadh is not going to side with Washington and will refrain from cutting off its oil exports to China. Because, the degree to which US imperialists (and zionists as well) infiltrate and subjugate their client states (so-called allies) is such that in the event these clients begin to seriously envisage balancing out their relationship to the US with one of America's competitors, then Washington will easily be able to act preemptively in order to discipline its vassals either through a palace coup, a "colored revolution", or even violent regime change if necessary.
Iranians are well aware of this issue, seeing how the former regime of the shah had been infiltrated by US and British intelligence services, masonry, zionists and their affiliate networks to such an extent that even after the anti-imperialist 1979 Islamic Revolution, these networks managed to keep in place certain covert stay-behind assets. Assets which presented themselves as opponents to the shah and as revolutionaries, managed to occupy official functions within the Islamic Republic but were in reality fifth columnists handled by the same hostile foreign intelligence agencies (Mossad, CIA, MI6) which had set up the shah's SAVAK in the first place. Such elements are referred to as 'nofoozis' or infiltrated agents of influence within the system, who are in fact working for the enemies of Iran and the Islamic Republic.
It's not going to be any different in Saudi Arabia. When comes the moment of truth, one phone call from Washington will suffice for Ryadh to interrupt its energy supplies to China, or else infiltrated networks will be activated to cause the necessary heads to roll at the top of the Saudi hierarchy.
The reality is that in case of a war or other type of major crisis opposing the US and China, it's Iran that China will be able to count on for its petroleum needs - not Saudi Arabia, no matter how much Beijing proceeds to expand its bilateral relationship with Ryadh. US imperialists enjoy an inherent technical advantage in this regard, insofar as their imperialistic ways lead them not just to systematically interfere in the internal affairs of client states, but also to encroach themselves in the security apparatus and deep state infrastructures of said clients. Whereas China, by contrast, has made it one of its foreign policy pillars to shun any notion of intervention in the domestic politics of partners (which is of course the more noble and commendable approach, but should not lead to short-sightedness as to the Washington regime's effective clout over its close strategic allies).
Now I've seen some persons opine that strategic level accords between China and the Saudis are a sign of growing autonomization of Ryadh vis a vis the US and that Saudi Arabia is now asserting its independence in the international sphere. However, this is not really so. What is in fact the case is that up to a certain point, the US regime is quite glad to see the Saudis enhance their ties with Beijing, considering how this might give the former some leverage in encouraging China to limit its support for Islamic Iran. And knowing that if the Saudis go too far, Washington has the means to punish them.
But planners in Beijing must be perfectly aware of all the above. Therefore, the motivations I can think of behind China's weapons deals and other sensitive engagements with Saudi Arabiaare twofold:
1) Economic profit.
2) China sees in Iran the potential to evolve into a genuine world power, with its reach extending beyond its own region. And world powers, even when at odds with each other, are not usually keen to welcome new members into their exclusive circle, as that would only force them to share a piece of the pie. Hence the desire to contain Iran to some extent, while at the same time preventing the US regime from having its way and toppling the Islamic Republic in order to plunge Iran into chaos, which would be detrimental to China's OBOR architecture.