What do you think about integration registration with Facebook and G+ without plugin?
From a personal view: that'd be nice
From a staff view: No. Not everyone needs it, not everyone wants it and it's too difficult to maintain. Eg Facebook seems to change their api every five minutes and we can't release a new version everytime they do so.
No. Would be nice but we can't take the time to maintain such features in 1.8.
There is a plugin for that
Third party login systems (OpenAuth, Google+, Facebook, etc) should remain in the realm of plugins. MyBB 2.0 should make such integration as seamless as possible.