It actually looks like they are doing exactly what they do at IAD - opening the lounge specifically for Priority Pass, likely with a lower level of service.

According to the PP website, the lounge is open 5am-11:30am daily. According to the SFO website, it's open 1:30pm-7:30pm daily, which matches their flight times (4:30pm and 7:30pm).

BA have been doing exactly the same thing at IAD for years. The lounge is only open for PP in the morning when there's no BA flights, with limited service/amenities. They then close the lounge, and re-open it again shortly afterwards with full service for their own passengers but without access for Priority Pass. I've used it a few times, and the breakfast offering was extremely mediocre (nothing hot, from memory just something like cereal and yogurt), however they did have showers!