Really glad to see that DL is continuing to pay attention to the SFO market. They have been leaving money---real money--- on the table here for years. The Bay Area is now one of the wealthiest regions in the world, and DL is the premium US carrier, it's a natural fit.
Perhaps they are hoping to really tap the transcon premium market and add even more routes. When people with the kind of money people here have are looking at 6 hours in the air, I suspect many are willing to pay to not sit in coach.
This also helps explain why they made such a big investment in the Sky Club here (showers, enhanced food, high end decor, etc).