We already have a Google+ Page, Chat, Meta, and IRC Channel, and several others. I don't see how adding a Google+ Community will really. In addition due to trademark policies we'll never be able to have an "Official Ask Ubuntu Community" on G+ since it's a Stack Exchange property (hence the Ask Ubuntu Google+ Fan page). IMO it's best to just join the Ubuntu Google+ community and discuss there.
In addition, this just becomes another noise box. IMO, it would be FAR better to create a sub-topic under the Ubuntu Community for Ask Ubuntu. That way the entire Ubuntu G+ community doesn't have to join yet-another-community on Google+. That being said I would ONLY want this to be a sub-topic on the Ubuntu Community if there was actual real demand for it. Not just want, but a demand. The same reason I've given for why we shouldn't have an Ask Ubuntu blog, etc.