I had been thinking that a bit myself, although until today I didn't have any advantages to post for it. If it were up to me, I would probably lean toward making it a class, since Shrinking Violet Otaku or Pervert Otaku seem to be a bit more rounded as characters than pairing Otaku with some of the archetypes from the class list. Also, depending on how they're played, there could be common elements between Otaku and Chuunibyou, so making them mutually exclusive for a single character might help with the overall variety.