The private area of the QueryHit is not documented, but (as far as I know) BearShare is the only client that uses it.

This private area, far from being debilitating to the network, allows developers to experiment with new types of information that may eventually benefit the whole network. You can think of it as a sort of trial area for new ideas, but most programs don't use it anyway. The standard for the QueryHits was developed in a somewhat seat-of-the-pants manner, but it works.

Also, if you look at the history of other protocols (such as HTTP), many of them were developed quite hastily (and even messily) in response to the pressing needs of the network.