Long ago Facebook Messenger was a dual client like Hangouts, for both instant messaging and SMS but it was removed later. Facebook Messenger’s SMS is again coming back to app. I don’t know how much it will be beneficial but still you might be able to add multiple facebook accounts in Messenger.
As you’ve seen in Google’s Messenger for SMS, Facebook’s new SMS feature in Messenger will do the same. So you’ll be able to send Facebook Message or SMS from a single application. Also in some leaked pictures a Blue Action bar and a Create new Button from Material design has been seen.
As Google already has the SMS messenger so there is a question mark on How it’ll be really beneficial to users.
And another feature Multiple accounts in Messenger is also coming soon but according to me it is also a bogus idea. What do you think about these? You can share your views here in comment.