As your last sentence says, nobody really knows. We have to see how they audit farangs, and see the result, and not just one, but many, to get a feel for their exact logic...!
This is many years away, I think most farangs, who do not earn in Thailand, won't fill up tax forms, and doubt many or any will be audited anytime soon, Thai taxmen are too busy collecting and auditing millions of locals, let alone farangs.
This very law was brought in for billionaires who make a killing abroad in dodgy businesses and countries without paying tax abroad, then bring the money in and use it tax fee..., not a few pensioners living on 1000 pounds a month...!
This will be the same tail as the other laws being enforced here, like buying land and houses using fake company, how many of those have they prosecuted yet...! Not many, despite all the propaganda...
Of course the tax lawyers and consultants looking for clients make this like it's the end of the world...! 😜