With iOS 8, Apple will now backup of all your photos. The limitations of Photo Stream seem to have gone away. Apple will now store all of your photos in iCloud, regardless of what device you take them on. iPhones and iPads can view these entire libraries, without having to download them to local storage. The photos stream in as you scroll.
Storage is only limited by your iCloud Storage. Apple has announced new cheaper storage plans to go along with the new philosophy.
Apple is also adding a whole host of color and other editing features into the Photos app. This includes things like color correction, brightness, cropping and more. These edits automatically sync across devices.