Federated Credential Management API
wicg.github.io
wicg.github.io
It would be nice if creating an account on a new website was as simple as a couple of clicks, and didn't require providing any personal information or anything linkable between sites.
I suspect, though, that websites (Relying Parties) will want some sort of guarantee that only one account per meatspace human is created on their site, to prevent Sybil attacks, and that might lead to there being just a short whitelist of acceptable Identity Providers (as is currently the case for much of the web).
Also, I'm sure that it will be designed to work in a backwards compatible way, i.e. the page can detect whether the feature is supported and fall back to a traditional username/password or social login system as needed.