This is scary. Email as an identity management platform is okay because the protocol itself is distributed. No one company holds the keys to "email." Sure, people have moved towards centralized email providers like Gmail, but many other individuals and companies still run their own email servers.

The scary part comes in when you think that if this technology becomes popular, new services might provide account recovery or identity management features solely through Facebook. As we've seen countless times in the past, centralization like this only makes it a better target for abuse by malicious actors (Facebook included!).