@John ******
the tax residency status is not changing. It's always been 180+ days in a year.
What's changing is that remittance of foreign income from previous years will be assessable. Until now, if you leave income for a year in the country of origin, it is exempt when remitted in Thailand.
This change is mostly to catch the rich Thais who have been exploiting this loophole 'forever'...
Many/most foreigners in Thailand, with foreign income, will be unaffected by this.
I doubt the tax department will even bother chasing down foreign residents, requiring them to register for tax, since they've never bothered in the past.
Again, the tax residency status is not changing, so anyone staying there for more than 180 days is automatically liable, but that has been largely ignored.