Facebook is testing out a new Facebook post type which would funnel viewers through to a private chat group on Messenger.

As you can see here, the new post type - spotted by reverse engineering expert Jane Manchun Wong - would essentially enable users to promote a private Messenger chat group, and link their connections through to it.
It's similar to the 'Join Chat' sticker Instagram added to Stories back in July:
Introducing the new chat sticker in Stories. Now, there's an easy way to start conversations with a group of friends right from your story. pic.twitter.com/A1An7d9TjJ
— Instagram (@instagram) July 2, 2019
Given the overall rise in messaging use across all social apps, it makes sense for Facebook to be looking at ways to better incorporate connection to more private discussion. It also aligns with Facebook CEO Mark Zuckerberg's 'the future is private' view of where social networking is headed, which is largely based on these same trends.
Depending on how its rolled out (if it's rolled out), it could also provide new ways for brands to spark discussion around their products and offerings with their most dedicated fans. You could ask people for their opinions, or pose a question related to your industry, and start a discussion on key trends. That would be dependent on it becoming a post option for Pages, which we don't know about as yet.
We'll keep you updated on any future updates on the function - but going on Wong's previous track record, it should be available in about 28 days time.