I guess they'll be shared between BKK, DM, Phuket and Chang Mai. Maybe they should think about internationalizing a few more airports. In the north east for instance. Lengthen the runways, put in customs and immigration, duty free, bus terminals etc etc. Link to domestic airports. Spread the load. Avoid the crush. Less travel out to the provinces. And Srettha's been banging on about promoting provincial tourism. A great opportunity, and not massively costly. Er, where's that 500 billion? Should cover maybe 10 airport upgrades. Great for local tourism. And thais can fly into China to visit auntie and nunc.
And factor in freight services, fruit, dried fish, all sorts.