Per Routesonline, Delta has updated their route schedule to include A350-900 service from Atlanta (ATL) to Tokyo's Narita Airport (NRT) starting on March 31st, 2019. This route will be replacing an existing Boeing 777-200 aircraft indefinitely. Further, Delta will operate this route on a daily basis.
Thrifty Tip: Not familiar with the new Delta One suite onboard the new Airbus A350-900? See our post on the Delta One A350 Suite in 14 Photos.
You can currently book this flight for only 40,000 SkyMiles oneway in economy, and 300,000 SkyMiles in the new Delta One Suite (I wouldn't recommend this redemption at this price point). Premium Select is listed as sold out, but my guess is this just hasn't been updated with the aircraft change. The seats appear to be open on the seat map.
It is great to see Delta continuing to add international routes on their flagship Airbus A350 aircraft. As the airline takes delivery of more of these over the next few years, expect to see them rolled out on more routes.