Originally Posted by Soju
I've never done it myself, but have read about other people doing this, and they claim that if THAI puts you up in the hotel, that you are escorted to the hotel without passing through immigration, and likewise on the return. So I'd imagine they'll do the same thing at the new airport. I think this is quite common at international airports around the world where transit passengers are forced to stay overnight due to airline delays/cancellations.
I have got STPC a few times. You get to choose the hotel and I twice choose the Amari Watergate in downtown, if the layover was long. You go through Immigration /Customs and contact the THAI desk outside the customs and they deal with it. No exception or escort through immigration.
If it was short, i choose to stay Airside and got STPC for the Louis Travern Day rooms.
I think in cases, when THAI has to provide hotel acco. due to overbooking or mis-connect, they do provide things like escort through immigration, but never happened to me so far.