Family sharing is long overdue, so it's great that Apple have finally got around to it. I hope they do it right:
A central iCloud storage for family members shouldn't just be partitions though. This will only work for me if there is proper folder sharing, and yes, photos library sharing (you should be able to decide which folders you share and collaborate). I want to be able to decide which album my pictures are stored in. If I take pictures of my kids, I want them to show up on my wife's phone, and visa-versa. If I take pictures for my own instagram, I might not need them to show on my wife's phone. etc.
If I save a Numbers document to a folder, I want that to be available in the same folder on my wife's iCloud. She should be able to open the document, work on it, update it, delete it, and amend it without having to save a new version and sharing it back. iCloud should sync the folder across devices naturally and without prompting. Shared folders need to act like a folders on a common server.
I fear, however, that iCloud family storage will just be about allocating storage to family members, which will mean that true collaboration and sharing will only work in the same way that it does right now - which is to say, not at all.
