I don't know if this would be possible to implement, and I already mentioned it briefly in another post, but the ability to network on WP.com would be awesome. By 'network' I mean the ability to visit like-minded bloggers through keywords that users would enter in their profiles under interests, favourite movies, books, hobbies. Also the ability to add other wp bloggers to a favourites account (perhaps that's already possible and I overlooked it if so forget that point).
But yeah, generally my idea is to create more opportunities for interaction.