Years ago, a company called "Over the Wire" put out a game and a small 28mm miniatures range called "England Invaded". That's the only pre-packaged Weird WW1 miniatures game I can think of.
Weird WW1 is a bit trickier than VSF: for the latter, a common thread is to take internal-combustion-engine creations like tanks and aeroplanes and retrofit them to the steam age. But WW1 actually did have tanks and planes, of course. So you are left with outright SF (death rays, robots) or the supernatural (Angels of Mons etc - Titan's Doctor Who comics recently mashed them up as the Weeping Angels of Mons - or the Black Max, who, as British comic readers of a certain age will remember, kept a giant bat in the fuselage of his Fokker Dr1).
One idea I have toyed with from time to time is Rommel vs Dracula. Rommel really was an officer in the German and Austrian armies' Romanian campaign of 1916-17. Scarab Miniatures' Great War range has a suitable character figure for him. It was the lack of 28mm WW1 Romanians that put me off last time I considered this.
Some other potentially useful ranges in 28mm are the assorted armed women in WW1 uniforms that are available: British and (historically justified) Russians from Minifigs, and Germans from Hinterland.
Edit: I forgot to mention: Hasslefree has a range of Halflings in British WW1 kit, while Eureka has WW1 Germans with rocket packs.