Interest on foreigners money in Thai banks is already taxed automatically. Started a few years back. That said...
Nobody knows anything because as typical, Thailand imbeciles spouting off another ill-considered BS money grab scheme without a clue and zero forethought of implications, existing treaties, exemptions, enforcement. Clear as mud, as usual.
Constantly scamming for ways to pay for their problems with others money. Never manning up, never taking responsibility and never solving their inept country's designed poverty/inequality from within and leading by example. Because it has nothing to do with that. That's the con, the smokescreen, the lie. Those in need will see a pittance at best and all the fat cats at the top will prosper immensely and widen that gap even further.