The lounge serves a subset of breakfast which you could found in MoMo Cafe. Therefore, this should not affect you at all. Consider other Marriott hotels usually not provide elite free breakfast in main restaurant, this instead should be a good move. I had stay there for the last 2 months, I agree the environment in the lounge was way better than MoMo. and I opted to eat in the lounge always becoz staff's services and never need to found/ wait for seats.

The hotel's occupancy was seriously affect by recent events in Hong Kong, I suspect closing the lounge for breakfast was another way for cost control. It still long way till New Year, things will change, no need to worry too much