A postscript on my JWM report. It slipped my mind till I was leaving this morning at 4:50 am and was joined in the elevator by a freshly showered thai woman who was leaving as well.
After I had checked in at the 16th CL desk and was in my room on the 18th I got a call from staff telling my that "if someone join you then extra charge will be added to your room charge, 500 bht". I was flabbergasted and ask them to explain, she repeated there will be an extra charge if my "wife" joins me. I stated that I was traveling solo and finished the call. Of note, I checked my reservation and I had booked a room for two out of habit and was credited with two breakfasts at the Marriott Cafe as well.
I get the issue with "joiner fees" and whether a hotel is "guest friendly" on not, but I have never had any hotel staff verbalize this to me as some sort of an advance notice. And given the travel through the lobby it looks like it could be a real revenue generator for them.