User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-7153535-20130812003603/@comment-4430596-20130814004704

Percy first made a hurricane in the Last Olympian, the same book in which we discover Nico can Shadow Travel. So, I don't think it's that unlikely that someone will develop a new power or we will figure out that a non-POV character like Nico has a special power no one knew about.