If you can pull this off, I'll seriously be your biggest fan. I'll be following this closely, for sure.
As for the fallout license:
Yes, Supermutants might be tough. But the fallout universe is not just limited to super mutants: Ghouls, slavers, tribals, the various city populations and their differences could all be modeled to great effect. Yes, the guns would be an effort, but certain guns would work great, the pipe rifle for example I could see being perfect. I think it'd be easy to lose track of how much is doable, by focusing on what would be difficult/impossible.
You might have to be selective, and creative in a storyline to exclude things that would be impossible, but I think that can all be done in a reasonable fashion, and end up with a great mod that's true to Fallout.
Finally, if Bethesda does become burdensome about the license, I would suggest using "Wasteland" instead to stay under the radar which was after all the game Fallout was based on.