The game can be played co-op.
MachineGames took the stage at Bethesda's… very interesting… E3 presentation, to talk about Wolfenstein. And while The New Colossus just came out last year, they still have some stuff to talk about, including the upcoming Switch port on June 29, as well as a new game in the Wolfenstein series called Youngblood.
Youngblood stars BJ's twin daughters, and takes a leap into the future into the 1980s, set in Paris and the entire game can be played in co-op (although they made sure to point out that the game can be played single player as well, so you don't need to play this with someone else if you don't want to).
We didn't get gameplay footage for the game (which is a running theme with the show), but what we did get was a pretty cool trailer, which kind of set the tone for what we can expect from the new game. You can see that trailer for it for yourself below.