The border is not the only problem. Airports. Airlines. Transport around thailand. Provincial lockdowns. Just the airlines maybe as far as October to make them have enough demand.
This has just been published on the BBC. "Scientists advising ministers on Covid-19 feared people would deliberately try to catch the disease or buy fake test results if "immunity passports" were introduced, newly released papers show. "I dont think anyone is going to trust tests or immunity passports"