p.s. SFO-JFK is my favorite domestic flight in the system, so would be sad to see p.s. go away, but I doubt this alone would be the factor to make the business no longer viable.

I think there is enough, shall we say, "money" in the areas to make it work. Around Thanksgiving I shelled out for Z class I had to get because there was no NC space and C was getting filled up and I had to sit next to my companion on an award ticket. So while this isn't the purchase of a 3-class F seat, it's still a Z which you can't get standalone on a 2-class plane. And for reference, that flight had on,y one unsold F seat left, too!