Whatever time frame THAI had for installing lie-flat business class seats in the 772ER, I am sure it has been derailed to some extent by the engine problems of their 788. They had to take one or two 788 out of service at any one time for the fix. So capacity is short. Now it remains to be seen if they will take one or two 772ER out of service to install these lie-flat seats in the upcoming high season, versus dealing with this issue early next year.

HS-TJR made last flight from BKK to DMK on Sept 14, for maintenance/installation?

The rest of the 772ER are in active operation.