In the dark pre-history of RPGs, they seem to bloom from the mix of wargames and fiction. In a wargame, you just need to consider "offense, defense, and movement". Pretty much everything else is "shtick"; the color and look of things. With fiction, readers want to identify with the hero of the story. Players pick a hero archetype, for example "misfit", "grizzled old timer", or "prodify", and that may modify their shtick.
The real question isn't "What has been done?", but "What do the players want?" The Golden Age comics are great, but they were written to a readership culture that no longer exists. Even dealing with historical events, like WWII, needs to deal with how the player's culture wants to game.
The other recommendation I'd make is don't overthink this. I planned one campaign for six months, and some miscommunications led to the campaign's demise. I much prefer to sketch out a basic idea, put in some flavor, and game it a couple of times. If players keep going then I put more into it.