Here are the Delta routes with Premium Economy class, nothing obvious works from SFO.
Routes with A350
From Detroit (DTW) to Tokyo-Narita (NRT), Seoul-Incheon (ICN), Beijing (PEK), Shanghai (PVG), Amsterdam (AMS)
From Atlanta (ATL) to Seoul-Incheon (ICN)
From Los Angeles (LAX) to Shanghai (PVG)
From Los Angeles (LAX) to Tokyo-Haneda (HND) starting on March 31, 2019
From Seattle (SEA) to Tokyo-Narita (NRT)
Routes with 757-200 (75H)
From Minneapolis/St. Paul (MSP) to Reykjavík-Keflavík (KEF)
From New York-Kennedy (JFK) to Reykjavik-Keflavik (KEF), Shannon, Ireland (SNN), Ponta Delgada-Azores, Portugal (PDL)
Routes with Refurbished 777-200ER/LR
From Minneapolis/St. Paul (MSP) to Tokyo-Haneda (HND)
From Atlanta (ATL) to Tokyo-Narita (NRT)
From Los Angeles (LAX) to Sydney (SYD) starting on April 1, 2019
From Atlanta (ATL) to Paris-De Gaulle (CDG)
From Minneapolis/St. Paul (MSP) to Paris-De Gaulle (CDG)
From Los Angeles (LAX) to Paris-De Gaulle (CDG) starting on May 25, 2019 through October 2019
Routes with A330-900neo
From Seattle (SEA) to Shanghai (PVG), Seoul-Incheon (ICN), Tokyo-Narita (NRT) starting July 1, 2019 through August 31, 2019
I learned from a previous post that there is a lot of confusion between Y+ (economy comfort) and premium economy (a separate class).