USA is not selling. f35 to KSA, as KSA is on the verge of the circle of trust. Europe has no 5th gen to offer. Zero chance of getting weapon from Russia as they are supporting Syria government. The only possibility is FC31. KSA knows it's time to diversify its military procurement so that USA won't take them for granted. It's strategical move not just a weapon procurement.
Even KSA didn't invest, China and Pakistan will keep push the project to its final success. We welcome KSA's investment, but it's not indispensable.
KSA's looking east policy will make Benifits for them in the end.
It was Pakistan that China and KSA could become friend.