Unfortunately I think the change to offering decent upgrades might have been short-lived whilst occupancy was low!
Just checked in for a three night stay and given a one category upgrade from the booked King Mai-Laa Suite to a King Mai-Laa Suite with Living Room which is worth about 300 THB per night. They said at check in it was for my loyalty (Diamond Ambassador) but I am booked through IHG Luxury & Lifestyle which would entitle me to that anyway (I saw the upgrade happen in the App weeks ago within 24 hours of booking). There are an unlimited number of rooms available to book of the next highest category which would be worth another 300 THB per night…
Perhaps upgrades are now focused on Inner Circle members.