Superheroes based on desires
I am working on a superhero setting in which if someone is desperate enough and utterly sincere in their yearning, a progenitor entity known only as the Giver appears to grant them superhuman abilities to help them realise their desires. This means that super-powered folks are almost never well adjusted, confident, or necessarily, heroic. A bullied child is more likely to gain powers than a community leader.
What system do you think would suit this idea best? I'm particularly interested in games that suit play-by-post well. I love FATE, but it is much too conversational (particularly during FP exchanges) to be quick to play in a forum setting. I'm currently considering Wild Talents, as it suits the slightly grim tone I'm looking at, but I'm not sure if many people know the system, so I'm not sure if I'd find players!
What system would you use for a superhero story about grey morals in a world where powers only recently arose?