The Fedorov Avtomat may be considered to be the "first practical assault rifle". It is a unique weapon and it was way ahead of its time. Although, it was used mainly in the Russian Civil War, it actually saw some service during WW1. It was very exotic weapon and too few numbers of it were produced to be used widely, however that is the case with the MP 18 also. Gonna be interesting to fight with the most primitive assault rifle in the history.
The BAR is already a well represented weapon in gaming and media. It is featured in every single WW2 game, however, the thing is this weapon originated in WW1. The BAR saw minor action in the last few months of WW1, but most likely it will be included in Battlefield 1 at some point due to its fame and the full-auto WW2 style crazed Battlefield 1 nature.
This... thing is dubbed the "worst machine gun... ever". Pathetic excuse of a gun. Basically, some Americans got to use them, only because they had shortage of actual weapons. The weapon was so poorly manufactured that its parts were not interchangeable between two chauchats. Well I guess the Chauchat will make it into the game because after all it is quite famous, yea as the worst gun ever, but as the saying goes "There is no such thing as bad publicity". Other than that, the Chauchat appears in most WW1 games or mods and has quite a dieselpunk appearance.
Battlefield 1 decided to get "full-auto WW2 style crazed" as mentioned earlier. They put in 2 early submachine guns, namely the MP 18 and the Automatico M1918. If that is the case, I have one problem... only 2 submachine guns? What a joke... and here is the solution, the Chauchat submachine gun. Exotic, rare + the bizzare prototype-ish dieselpunk look. All checked. The gun was tested by the French during WW1, but was deemed to have too low range and was abandoned.
Another prototype and exotic gun (that was actually prepared to be shipped to the European battlefields of WW1, but ironically that happened the day the war was over). You want the classic Tommy gun in your WW1 game? No problem, just slap in the prototype. Also this way youll have 4 submachine guns, that makes more of a weapon class rather than only 2 I guess.
An exotic semi-automatic revolving shotgun of German origin. Designed in 1899, however, it was put to production only after WW1. Only 100 of these unique shotguns were ever produced but what? Enough with the idea that only the yanks can make shotguns, let's see some German attempts in this field.