The way I see it is this, the only thing that has changed is when you bring money into Thailand, nothing else.
Previously if you brought money into Thailand in the same year, you had to file a tax return and pay any taxes on it.
How many expats have been bringing in their pension in the same year and technically should have been filing a tax return and did so?
I think I can hear a pin drop, no one. Most didn't even know about this and lived here for years and no one filed a tax return and the tax dept never came knocking on their door, in fact it wasn't even mentioned in the media or any expat advice sources... up until now.
I don't even think the tax debt has even thought a lot about us expats regarding taxes, the change from deferring bringing in money any year from the current year was to catch wealthy Thais escaping taxes.