Battlefield 1's final premium DLC was released today. It has River Somme, Paschendaele, Caporetto, and 2 aerial combat maps. One over London and the other over the Alps.
The experimental RSC SMG was added, as well as the experimental Howell rifle, and the MG08/18, the Ross rifle and the American Enfield. Don't forget the Webley, either.
I believe they have more in store for us, though. A melee weapon, the broken bottle, seems to have not made it to the release. Also, a few guns have been datamined from the code of the game, like the Reichsrevolver.
Dice also likes giving out free DLC's when a game begins to get old. I wouldn't be shocked to see Tsingtao, Vimy Ridge, or Serbia