the last time i was in the CX lounge at SFO in late october--it was empty--but did start to fill towards the time of my departure (the later a380) but at the time the BA lounge was still open, i was just directed at check in to CX which i knew was better than BA anyhow.

at that time of day, half of the lounge was "closed" meaning they had a rope up blocking access to one side which they did open up towards my departure time as the CX pax presumably started to arrive for the evening departures. it is a rather spacious lounge, so would be surprised if they severely limited access...but i'm sure that may change in coming months as OWS and OWE's try to use CX first!