It occurs to me that there are only two countries that tax worldwide income; the USA and Eritrea of east Africa.
Americans get a foreign tax credit on their US taxes for taxes paid in a foreign country, so no change for them. I don't know about how it will work out for Eritreans.
For the expats that hail from countries that do not tax their citizens if they are out of the country for a specified time (usually it's 180 days or more) in a calendar year, they have been enjoying tax-free living while expatting in the LOS, in many cases, for decades.
While I sympathize with those who will find this a challenge to pay Thai taxes, the saying of "there's no free lunch" comes to mind. And the argument that these people contribute to the Thai economy in other ways, well, so does everyone else.
Whatever the case, nobody should have to be double-taxed on the same income. I surely hope that if this issue arises, it gets ironed out such there is no double taxation.