Agreed that alcohol would be one of the main factors, and that would need to include duty-free sales at the airport. Foreign cabin crew and frontline customer service staff would be relatively cheap and make a huge difference. Jeddah with a few billion dollars spent on it to upgrade the airport and build a few tourist attractions could be a reasonable stopover, or even a tourist destination in its own right, especially in winter.
Qatar realized that Doha can't compete with Dubai as a stopover or tourist destination and positioned QR as a premium airline with highly competitive fares instead. An attractive option for someone who just wants to get from A to B.
Tehran is actually very well positioned for a hub, and if it hadn't been for the Islamic revolution, Iran Air could be a major hub airline. Back in the 1970s they were a decent outfit.
Time will tell how serious the Saudi rulers are about modernizing and opening up the Kingdom, they may follow the UAE road map. Already they have allowed cinemas, women driving and El AL overflight rights, which would have been unthinkable not too long ago.