For those not aware, Google+ allows you to share your posts publicly or to any number of circles, which are user-defined collections of people that they follow the posts of. This was meant to allow for privacy where, for example, if I have some family photos I want to share, I could share them with my family circle rather than publicly (as in Twitter) or with all of my connections (as in Facebook).
Jeff Jarvis mentions that he uses circles to limit sharing out of relevance not privacy. That may mean that there are some posts he is fine sharing publicly, but doesn't because it would likely be noise to most of his followers. An extension of the circles concept would be some notion of sharing within a category (or topic or tag).
The specific example he brings up is that he shares specific things with journalist and tech circles that others might find boring. But, what if people had the option when circling Jeff Jarvis to follow all posts, his journalism posts, his tech posts, or any other categories he defines? Just as you would choose which circles to share your post with, you could also choose which of your category streams to share the post into.
This is probably unnecessary for the ordinary user, but for the more followed users on Google+ (like anyone on the TWiT network), who have followers with a wide range of interests this might be a nice feature to make your content more relevant to the people who knowingly followed a particular interest.