By mid to late 21st century, relations between Pakistan and KSA are likely going to become colder. Pakistan's economy is quickly growing, as is its population, which will likely lead to Pakistan asserting itself far more deeply, in the Muslim world. This will no doubt lead to Pakistan and KSA butting heads, as both compete to lead the Sunni Muslim world.
Likewise, Pakistan's relations with Turkey and Iran are also may become difficult, for likely the same reasons, as the later two also are trying to become the undeclared leaders of the middle east and the Muslim world, as a whole.
With KSA, it will be very difficult to avoid such an eventuality, if not down right impossible; Shared historical geopolitical and military cooperation, and culture will likely delay any sort of degradation of ties, but it will be unlikely to stop such an occurrence from happening. With Turkey and Iran, things will be easier, but Pakistan will have to build and define its relationship with both the Turks and the Persians now. With Turkey, Pakistan has the benefit that it won't have to directly compete with them, as both are geographically far apart, with similar noncompeting interests and different immediate priorities in their respective neighborhoods; both nations will have time to adjust to each other's geopolitical needs and interests, hopefully delaying or even halting any sort of downgrade in relations.
Despite what it may seem like at times, both Iran and Pakistan are quite sensitive to each other's interests, considering they're both immediate neighbors. CPEC has also helped to bring both nations together, as Chabahar seems to be stuck in its tracks, despite India's assurances of its financial and political support. Right now, the two major issues between Pakistan and Iran seem to be border management, and Iran's conflict with KSA, which both Iran and KSA seem to be actively fighting within Pakistan, through the use of militias, politicians and sectarian extremist groups. With Iran, Pakistan needs to incentives economics, so that Iran will see more benefits from supporting Pakistan geopolitically, instead of competing against it, this may be the only way mutually beneficial way to pacify Iran.
Of course, these are simply my own views, so take them with a pinch of salt.
The issue has less to do with the alliance and an overall change in the way the Kingdom is run. Unlike the Khaleejis, the House of Saud has been blind to any walking away from oil until recently. They are only now realizing in the past 10-15 years that they need a Saudi based workforce at all levels of society rather than one based on immigrants.
There is also a need to keep a loyal population as regardless of alliances between the key Royals & Establishment republicans within the US, the majority of the population and even many of the 4000 or so princes resent it on religious-political grounds.
One way is to keep the ancillary ruling class flush with money & out of politics while letting the Saudi Citizen enjoy lots of privileges with little work(
although this is a misnomer as a lot of Saudi Middle class and lower-middle class work a lot to survive).
Coming to the alliance, there is nothing Islamic about it besides that fact that the leader's of participating countries are circumcised. The focus here was to form a bulwark against Persia who are using both direct and asymmetric means to assert themselves again- as such a extension of Russian control (
recent protests in Iran highlight both real and financed anger at Russia).
Does it not bother anyone that despite all the hoopla against the Saudis(and their GCC kin), they just purchase advanced equipment like no one's business?
It is no accident. First, it pays to have a heavily armed Arab front against the Iranians(and by inference- Russia) so that if push comes to shove; the US can leave the middle east a cold-war esque combat zone while it turns back to focus on the two eastern power houses of Russia & China.
Second, the billions poured in assist the Defence manufacturing complex & allows the money sent to pay for middle eastern oil to return back home.
This alliance was an effort to try and get some military momentum with cannon fodder from poorer countries like Egypt, Pakistan & others into marching into Iraq to "protect them from ISIS" and creating a bullwark against Iran.
Thankfully, while one can accuse Pakistan's establishment of great many a folly; in this case they read the situation well and are still not at all keen on taking on Iran directly.
Our focus is now on making us a trade hub for central asia and in turn being able to create a positive gravitational effect of foreign policy to attract countries from the middle east including Iran to become stake holders in that trade route. That stake allows us to use influence and eventually make Afghanistan succumb to some form of quiet resentment where it feels isolation or at the least anger from its neighbors in case it tries to act against us at the behest of India.
In addition, with CPEC we might eventually be able to create a stable growth in the economy(
if possibly imploding eventually in 50-80 years) to finance a strong enough conventional force that is able to last beyond the current projected 10-15 days against India.
Right now, the game is being planned for 50-80 years; the way the world is going, not many can see or plan beyond that.
Disclaimer: The above represents my opinion based on observation of world events & verifiable news sources along with informed opinions. IT may or may not represent reality.