Hi Michael!
I don't have any news on the Facebook integration, but I can provide some insight into why Twitter was done first.
You're right--Twitter is a more natural fit for contact centers (it's easy to view a tweet as a type of interaction), and in addition it was released first because it was simpler to work with as a prototype from a technical perspective. The core concept was to be able to route social posts to agents so that agents could respond. Twitter provides a public stream of posts, while Facebook only allows you to interact with posts you that own, so finding and routing posts to agents would be trickier. Facebook also has many more kinds of posted "objects" than Twitter, which has just one--the tweet.
In case you haven't seen it already, here's the help landing page for Social channel management: https://help.mypurecloud.com/articles/about-social-channel-management/, which might also provide some insight on the goals of social channel management.
Please let us know if you have any follow up questions :)