Working on a more thought-out post on this but I thought I'd get some feedback before diving too deep.
How about an Identity #coop ? A simple but solid #oauth identity provider that also advocates for it's inclusion as an idp to the services used by its members.
Convenience of single sign-on with the smallest possible security risk surface area and, being a co-op, members (users) decide what data is collected, shared, etc.
I have more but I'll stop here for now :)