<link rel="openid.server" href="https://indieauth.com/openid" />
<link rel="openid.delegate" href="http://mynamedomain.com/" />OpenID has gone the same way as XMPP, a good open and decentralised protocol lost to proprietary social networks.
https://stackexchange.com/users/login https://bitbucket.org/account/signin/ http://openid.yahoo.com/ still responds, surprisingly. The wordpress openid plugin is still around.
1. The NASCAR problem. Listing out every popular service does not guide the user through the login process.
2. The lost NASCAR problem. I know I signed up with one of these services but which one for this site?
3. The abandoned service problem. How do I access this site after my identity provider closed shop or the service I was using decided to stop supporting OpenID?
4. The redirection dialog problem. What do all these dialogs mean and what access am I granting to who?
5. The phishing problem. The default experience lends itself to teaching people to type secrets into popups / redirects coming from other sites.
6. Nobody wants to be a URL; email is king here. The support for email came late in the game.
7. The double registration problem. I signed up with OpenID which gives the site my basic profile but I still have to "finish" registration by giving more information.
There are many other issues but those are the big ones to me.
Your "ultimate solution" will just become another on top of the "ultimate solutions" listed as the services you indicated on your post.
Your idea seems too narrow to address a mass-market.
The tools that exist are already serving niches:
- Bugmenot - to bypass signups where something important is needed behind the signup-wall but probably not an account you'd use for amazon.com
- Quick signups = social login . Most people are content to connect to sites via Google/Facebook login, which avoids the entire signup process
- Lastly, don't forget OpenID - it died recently and was an attempt to unify the login process. Probably exactly the use-case for you.
Truth be told, site-makers have signups because they can and do so because they want to capture data from users for "important" advertising, user-data-selling, etc.
So long as users are happy to sacrifice some data for a 'free' service, this is the model the internet will continue to thrive on and signups will continue.
If you want to go ahead and try to solve the problem for yourself, it may be worth it. For the average user though, this is another non-problem in their quest to use x-social-cool-new-app that requires me to just login via Facebook to so I can "share" stuff.
Good luck!