A post-apocalyptic game set in the 1920's. Thread

I've had this idea for a long time... basically a video game of some sort set in an alternate reality, where World War 1 continues past 1918 and well into 1920. However one day, the Axis powers releases a world wide gas attack, the basically ends the world. Unless you're above 11'000-14'000 feet, where the gas cloud recedes after the first few hours of the attack, meaning that some people are able to survive. However the cloud lingers at lower elevations for quite a few years.

The game would rely mostly on trains to get around, like mobile bases that you can modify, use to explore and gather/store resources. The game would be mostly historically accurate, with a small touch of diesel-punk thrown in. And as the game progresses, the more fantasy post-apocalypses it becomes. Such as how things get modified, and the mutation of monster in the gas.

Over all I think this would make for a interesting open-world, simulator survival game. Overly ambitious and far too impossible for any to want to make, witch is why no such game exists. But I like to throw my ideas around and see whats stick before hating myself for them.