Why use fictitious battles when, with artistic liberty we can just take the existing ones and make them more exciting for a game? Why have reskins of already pre existing maps instead of trying to make new ones that may become fan favorites down the road?
If you want an Operation Metro set in WWI you can have that with the tunnels that both factions dug in attempt to sabotage each other. Much like the Lochnagar Mine as MilsurpShooter suggested. Tunnels and explosives could be the name of the game. And I’d rather expand on that idea and other WWI based ideas then just taking already made maps and revamping them with a coat of WWI paint.