We had a similar problem at Yahoo! with BBAuth and OAuth. Developers started out initially building an application that needed access to (for instance) Yahoo! Mail. Unfortunately, there's no way in the Yahoo! Developer Network to "upsize" an application ID or consumer key after it has been created. You can't go back and say, "You know what? My application could be 2x as awesome if I added Yahoo! Address Book support.…
the "scope" parameter that google included is actully from the OAuth 2.0 spec (still in draft iirc). There are a lot of improvements in OAuth 2.0 which are worth checking out, but this is one of the main ones