But isn't the OP is talking about a step towards that common API you're looking for? Wordpress duplicates a lot of FB functionality, and the Jetpack identity f

But isn't the OP is talking about a step towards that common API you're looking for? Wordpress duplicates a lot of FB functionality, and the Jetpack identity framework provides tools for applying user-controlled permissions to accessing the data exposed by those functions. It isn't hard to imagine that exposure taking the form of an API, or the expansion of that identity framework to Google / Twitter / Open ID authentications. Doesn't sound like you necessarily disagree all that much.