It looks like it's currently planned to revert back to a 787-9 for Winter 2020/21.
Last week I booked a redemption in CW for September and it was wide open on most days for business and a good number of days for First.
correct will revert back to a 789 for winter and there will be the usual week Christmas break for the service. Loads in the winter tend to be light if there isn’t a conference on in the Bay Area. Having said that the flight is becoming popular with all us ex-pats who live in the Bay Area.
TBF SJC has always had good Avios availability even despite BA.com including San Francisco in the title on the search engine. I managed to snag three J seats with 6 weeks until flying last month and family members have even managed to get 2 J seats on three days notice.
I love this service I can be at my front door within 55minutes of landing- that includes baggage collection and a 20min drive home beats the hole that is SFO arrivals.