Thailand cannot legally rewrite the DTA with the US, as it's a bilateral treaty.
But your understanding of the tax consequences of the DTA are not accurate.
For example, the US gets first crack at taxation of Social Security and other income streams generated in the US, but then if Thailand's marginal tax rates are higher, Thailand would tax the income streams at its tax rates, minus whatever was paid to the US. The DTA only provides for coordination of taxation between the two countries.
If you are a US citizen and a Thai tax resident, you are going to pay the same tax amount in total (to the two countries ) that you would pay Thailand if you weren't a US citizen.
If some Farang in the village is forced to file a tax return, they would be at the mercy of whoever they face in the local Revenue Dept. Once you are in the Thai tax system, it's almost impossible to get out.
Also, I know enough about DTVs and Thai tax regulations that for the poor bastards that have to file Thai returns, most of the tax advice given here is either wrong or irrelevant. I would go into it more, but I don't believe that most Farangs will be filing tax returns next year