The ML activities at Facebook seem to be focussed on delivering content and advertising optimally to users. They can determinine which posts or adverts you might 'Like' based on your friends choices, or those of other similar groups of users found by various demographics and metadata. It's right there in the research group page you linked:
> "We strive to find ways to deliver more engaging content in News Feed, rank search results more accurately, and present the most relevant ads possible."
I think it'd be a pretty poor use of ML and AI to use it to try and guess the gaps in your profile, and then fill them in. Of course I'm sure they try and show you content and adverts based on what they believe your demographic profile might be, but these beliefs are purely internal to the algorithms that make the decisions as to what to publish - they aren't used to populate your public profile.
In fact, Facebook want the profile information to come from you and for it to be as accurate as possible - to help those algorithms. It wouldn't be sensible or useful to just set your profile fields based on guesses, no matter how clever the ML behind it. As I said before, I think people ascribe too much intelligence to the way Facebook handles personal information - it isn't magic.