Thai authorities are absolutely & 100% paranoid about even 1 case in Thailand & as a result of this paranoia I suspect they will keep borders closed (except under very very strict/impossible(?) conditions) until a vaccine is found.
Of course, no one knows for sure exactly what whacky ideas they may come up with (there have been plenty of those!) but until then the doors are closed.
We had planned many international travels ex-HKT this year but since March have travelled exclusively in Thailand as we know that if we leave we cannot get back in (easily if at all).