Someone from r/hockeyjerseys is claiming to know a guy who has this from Adidas with NHL teams that are getting new third/alternate jerseys for the 2018-19 season. The Pittsburgh Penguins are among those listed.
It’s not much to go on, but it makes sense. Aside from Stadium Series jerseys, no NHL team had a regular alternate jersey this season (2017-18) as the league switched from Reebok to Adidas jerseys. It was long reported that adidas would slowly re-introduce new alternate jerseys for teams after they established the normal home and away sweaters.
The Penguins will take on the Flyers in Philadelphia at the Eagles stadium in February 2019 for a Stadium Series game.