I know there is Open Login plugin which can be used for other login options but it is no more developed and it is causing problem with SnowFlat theme.
Moreover, if we need Q2A to go big then it should provide some basic plugins which are needed by almost everyone. And who will not want Facebook, Twitter, Google logins out of stock?
This is what I think... Other then this, if Facebook login is removed with Open Login then that will also be great, but that plugin is itself heavy that's why I mentioned the other method first.
After all Facebook plugin was also introduced at sometime when it was needed most and now other login methods are also needed. So what do you guys think about this?