Yes, you're right. GoPro does already make an actioncam harness-mount for dogs (as does Sony, for that matter). The currently-crowdfunding PetNow system, however, offers a few additional features for people wishing to see the world from their canine's perspective.
PetNow consists of three parts: a "soft, lightweight, breathable" harness, a Wi-Fi-connected HD video camera that quick-mounts onto that harness, and an iOS/Android app. And while that setup certainly could be used for getting some cool point-of-view videos of your dog's adventures, it's intended more for keeping an eye on what Rover is up to when you're not home.
Utilizing the app, users can view the camera's live-streamed 1080p/30fps video at any time, wherever there's internet access. They can also talk to their pet via a two-way audio system, although it's hard to say if the dog will recognize the voice coming out of the camera as that of its owner. Additionally, if the animal wanders into an unlit part of the house at night, the camera's night vision system will still show what's going on.
Should users wish to record and then share any of the video (or take still photos), they can do so via the app. And if they want to instead go for a more traditional dog-monitoring setup, in which a stationary camera watches over one room, the camera can simply be removed from the harness and set in an included base.
PetNow is presently the subject of a Kickstarter campaign. Assuming it reaches production, a pledge of US$79 will get you a system, with your choice of five harness sizes. The planned retail price is $169.
You can see footage shot with the setup, in the video below.
Sources: Kickstarter