I... have not read the 9 pages of stuff before this, so apologies if my two cents have already been talked about, but...
A book series called Broken Empire. Weird High Fantasy in a world that is a future version of our own where an apocalypse happened that brought supernatural stuff and reshaped the world completely. It's like Game of Thrones, but with nuclear devices and such.
Fallout. Just. Please. Not any specific Fallout game... just a game set in that world, with those factions. If anything, I'd think that the early games would be better to draw inspiration from, as the lore was actually more tight before Bethesda came along. Note: I also love the Bethesda games and their additions. I just think the earlier games would make for better inspiration for a MU*, specifically. Bonus points if I could get a game that actually combines the early Fallout games with the Wasteland games for maximum win.
While I'm going on about post-apocalypse... Mad Max. The iconic wasteland. Doesn't get much better. Also, Into the Badlands, because it's how I imagine Georgia looks in the world of Mad Max.
American Gods - This would be fun to create in the vein of a WoD/CofD style game, with the base characters being essentially tulpa, or thoughtforms given life through belief, and getting powers associated with the beliefs people have of them. Maybe a bit like Scion or something.
Assassin's Creed. It has a narrow focus, maybe, but the Ancient Aliens aspect of it is pretty killer and you have this ages long shadow war between two factions that is every bit as political as it is parkour and throat-slitting. Set it in the modern day, with competing factions using the various Animus style machines to access history, and you have a game that can be an number of things, while still fitting within the same theme. Alternatively, just pick a period of history and roll with it. Let's see the Fall of Carthage through the eyes of the Templars or something. Good stuff.
Diablo - Fantastic lore, high fantasy setting, larger than life heroic characters? I just think this could work surprisingly well as an MU*.