It's a question of how important market segmentation is today given all the powerful distribution channels that exist.
Facebook today = Instagram.
Regardless of the constrained market (Colleges, Mobile, Format Type (Ex: Video) you focus on, you need to have it and create a great social experience.
The truth is, the only thing that will disrupt Facebook will either be a Photo or Messaging product, more likely photos (since their language is universal)
So maybe not colleges, but maybe photo site w/ a focus (ex: Pinterest), or format (ex: Vine, Cinemagram).