It's actually LAW. It's in the Traffic Act. A temporary visitor (of no defined duration) covered by an international treaty can use their home licence and IDP. It appears you are trying to massage length of visa into licence requirements, whereas it's actually type of visa.
Not just digital nomads, but retirees, dental appointments, cooking classes - you name it, people have got it! I'm just as curious to know who in the government has told you it won't be around in five years! 😂
Correct. The Thai Law states "temporary visitor" so the IDP is valid until the visitor leaves. However, the international treaty suggests 12 months, so that would be the maximum time. I understand Japanese Traffic Law actually stipulates a time period of 12 months for the IDP.
Not that simple. To enforce a law there must be a specified number or situation otherwise the law is meaningless. UK Visitor Visa for example is six months. There is nothing in Thai law which suggests a period of time, rather it's situational and defined as "temporary visitor".