Considering the popularity of Stories on Instagram, Facebook Stories has not been that popular and this may have contributed to the company's has made a decision to streamline its Stories section. The fused experience is now simply called "Stories", and any photo, video or slideshow you upload appear both on Facebook itself and the Messenger app. Its addition could make things even simpler, but as with any experimental Facebook feature, it might or might not see a wider release. You can make your post public, visible to both Facebook and Messenger friends or visible to Facebook friends only. Instagram is already pretty well integrated with Facebook, so connecting both the services' Stories feature shouldn't be too much of a technical problem.
Meanwhile, Facebook is also launching Facebook Stories for its stripped app for the developing world, Facebook Lite. According to TechCrunch, not only will Stories between Messenger Day and Facebook be consolidated as of today, but Facebook is also getting rid of Direct, an ephemeral messaging feature. Across its four main properties Facebook, Messenger, Instagram and WhatsApp Facebook had a Stories feature within all of them, independent of each other. How many people are now using Facebook Stories and the cross-posting feature isn't clear; it is clear, though, that many Facebook users aren't interested in Stories given how infrequently they show up (brands aside).
The company is now making some changes to Stories with the aim to get users to actually start sharing their days with their friends.
Update: This post has been updated to clarify Stories from Groups, Events and Pages will not be available in Messenger.