Lockdown is the last thing they would want to do. But I believe they would do it if hospitals get overwhelmed by Omicron. (Which at the moment does not seem to be happening at all). The future is not predictable though...so only come if you are able to roll with the punches. Be ready for anything.
Approved(QR issued) = OK to fly. They added 2 additional covid tests after you arrive. That's it for now. It could be different by 21-Jan. Just stay tuned in case new requirements get added. It's only been a week since Omicron was identified here...they are bracing for its impact, so I expect week-by-week revisions as things evolve.
They are meeting on Friday to make a decision about which countries to reinstate 14-day quarantine, and which countries will remain eligible for Test&Go.
Sometimes if the person intends to move onward to another province (ex: Samui), some of those province will want to see that negative report from your hotel.
It's not without precedent. China already does this. Every citizen is tracked and scored. However, I don't see the rest of the world following suit on China's example. People would revolt.