Just being able to read, write and serve files from a directory would be pretty awesome - I envision apps like instagram or vine that sit on top the bittorent sync storage. This way all the media always belongs to the user; and we have none of the pesky T&C's where the company owns the user's content. Taking it a step further and being able to "serve" said files directly from the storage would be pretty damn amazing - being able to a build an app when you don't have to worry about scaling / bandwidth; and let the p2p protocol handle it.
