An update on Keybase, since it was chosen as the example. The API now supports field declarations. For example, these all work:

   https://keybase.io/_/api/1.0/user/lookup.json?username=chris&fields=basics,pictures
   https://keybase.io/_/api/1.0/user/lookup.json?username=chris&fields=basics,pictures,profile
   https://keybase.io/_/api/1.0/user/lookup.json?username=chris&fields=basics,public_keys

This change was intended from the beginning, but we are still in alpha. It was a quick addition, so the HN post made it timely. The nice thing is that this isn't just a client-sensitive change. Loading a user's info is module, so those above examples should be faster and less work for our server than getting everything about someone.