Facebook did a half-hearted push towards a more messaging focused experience during the conversational boom, but didn’t manage to make any inroads and abandoned the effort. Whatsapp could have been the beachhead but with the original leadership and vision gone, nothing interesting will happen there. Instagram (also without original leadership) is slowly being turned into sludge by whatever PMs Facebook has left.
There is room for something new to kill Facebook, that is if they don’t buy or copy it in time.