It would interesting if high levels of radiation sickness over the span of a few days would turn the protagonist into a ghoul, allowing for a different set of perks and a new play style. Seeing how differently NPC's react to you being a ghoul, maybe even leveling up over time into a glowing one or even a feral ghoul if the player chooses to remain a ghoul.
I know a cure was never mentioned in the Fallout lore, though maybe a quest or a way to cure ghoulification if you changed your mind early on.