my feeling on this, since you have told me Sam might be taking on a darker tone, that this will counter balance Sam's abilities.
I also think this will give them both good character development, having to fight through this to stay brothers, fight through their fears, give some angst and comedy to it as well.
His abilities won't be as strong as Sam's. I also think it would be kind of like when Castiel fought against Alistair and Cas nearly bit it till Dean saved him.