The musical chairs with the immigration desks has been stable for a number of months now, First and Business class passengers (with their boarding cards) should enter the immigration queues to the far right, along with Thai passport holders, the queue then divides between Thai passports and premier passengers. With this in mind I think it is pointless for a member of Thai staff to escort you from the plane. I know Qatar are moving (? have moved) to the S terminal but their lounge is moving with them.