Having a united Arab state that spans all of Arabic-speaking Asia plus Egypt and Sudan, would be very difficult though not impossible to accomplish. The POD would have to begin somewhere in the mid-to-late 19th century.
First of all, you would need to somehow prevent Britain, France, Italy, etc from annexing all those various Arab territories they took from the Ottoman Empire. Then, you would need to have some brilliant Arab monarchs/warlords with a pan-nationalist vision to unite all of Arabia (ala Germany or Italy) engage in a successful campaign of anti-Ottoman rebellions and conquests of other Arab states.
I admit that I am not sure about all the exact details of how this scenario would work out. But if done correctly, an Arab super-state would probably be very economically prosperous because of the abundant oil reserves and control of important trade routes. If the government of united Arabia isn't too corrupt or incompetent, then the Middle East would be (relatively) much more stable than what we have now in the real timeline.
The potential problems for this giant Arabia would all depend on the type of government it gets; theocratic or secular, monarchy or dictatorship or democracy, etc; but most importantly, if the government is competent enough and has a strong military to mantain order. If ethnic/religious minorities like Shiites, Christians, Kurds, etc are treated decently and fairly enough, then there's less risk of a violent separatist rebellion.