this

Considering the fast-paced nature of most FPS, and that the most famous WWI scenarios were on the Western Front (the war on the trenches was incredibly static), I suppose they don't translate well from a gameplay perspective. They could focus on the african front and the middle eastern front, but those aren't nearly as well known as the western battles like Ypress, Somme, Arras...

I watched the video muted, so is this multiplayer only? Didn't see any singleplayer footage.

This.

WWI was interesting for many reasons but as far as translating that scenario into gameplay, it woud be a difficult thing to do. WWI was this weird era in warfare where they were developing 20th century weapons while still using 19th century battlefield tactics, which led to a slow, bogged down war that ended up killing a lot of people in a short period of time. With WWII, they figured how to properly integrate the new technology of tanks and planes into the battlefield more properly which is why the Germans achieved more early on in the war in a matter of weeks and months than what any army during the first world war could achieve in four years. That also translated into more desireable gameplay.

Also, maybe I've been missing something, but is there a demand for more WWII games? I remember during the 6th generation where we got a bunch of them. People eventually got burned out by them. Could they be coming back now that a lot of time has passed and many people now have an interest in anything they see as "retro"?

You need to play Devil's Third. It have pretty cool WW2-esque sections.

Yes but I think it would be a bigger breath of fresh air plotwise ... 

While you may not be able to sell the game in terms of level design you could at least sell in terms of more original content ...

Maybe you could do something similar to Spec Ops The Line, and focus on the horrors of war and the shock the soldiers suffered from its initiial enthusiasm.

I was interested until the point that i heard that it was a multiplayer game

Where are single player adventure FPS games ala Unreal and Half-Life. I will kickstart Un-Life.

https://www.youtube.com/watch?v=BAzQd90S-fE
They reached their Kickstarter goal so expect more information on the game in the future.