How'd it be if Bethesda came up with the most uncreative idea in centuries and even market it by that:
SUPER MUTANT GHOULS
THEY ARE THE LAST OF THE MASTERS ARMY
Having been first generation mutants under the leadership of the master, those poor fellows have experimented with FEV and they could steal the last vats of this valuable substance out of mariposa. After having realized that they could not possibly regain their ability to procreate (also the use of FEV would even further separate their individual genomes, so that they couldn't interbreed sucessfully) and after all their attempts to recreate super mutants like the master had done resulted in babbling dumb-dumbs, no proud members of supermutantkind, the last of the masters army (as they called themselves, TLOTMA is the abbr., yeah, you say it like one word) decided that they could do something about their situation: Adopt the ability of ghouls to be healed by radiation. That way they could essentially become immortal, so that supermutants would survive, and never leave the genepool.
But they adopted the ghoul's looks as well! How cool is that?! Now there are SUPER MUTANT GHOULS in the lore. Many characters in the game could remark how much of a dumb/great idea that is. That way you make something uncreative creative. Just [censored] on creativity and work with what you have now.
Anyway, the TLOTMA faction would be at war with some holy scientists, who try to purge the water in the region of its evil irradiation. TLOTMA cannot allow this! They need the radioactivity!! With Gatling lasers in their mighty rotten fists, they get down to action. They breathe brown clouds and wear supertechnological glasses or visors, that allow them to see radiation, so they can take advantage of it while in combat.
So what's the only thing (this is not true) that can kill a super mutant ghoul? Another super mutant ghoul. So they're also at war with themselves. One faction inside TLOTMA could be accessible and even befriendable by the PC.
What else can be said about this matter?