It'll be interesting to see how the Arab states will diversify their economies in the next decade. There's really not much to exploit there except oil, so unless they pump out enough money to basically rest on their investments in perpetuity I'm really not sure what to expect.
Joke apart, how would they make money with solar energy? Oil is a very limited resources that can be transported very easily. Every country in the world needs oil but only a few country can supply it so the business model is extremely straight forward: export oil to the countries that has the money to buy it.
Now what is the business model with solar energy? Every country in the world has sun and electricity is hard to export over long distance so what are they doing with it ?
The wisdom of these gigprojects in the middle of a desert aside, it would be awesome more governments would stop trying to run themselves into the ground for profit. Because who the fuck is benefiting if a country is taking more in taxes then they are providing their citizens in services?