That isn't an advertisement. People legitimately want content from Pages to show up in their news feed. If it was an advertisement, it would say "Sponsored".
But yes, ads are not out of the question in the future.
To be clear, Facebook doesn't tell any advertisers any information about any users. Advertisers tell Facebook what kinds of people they want to see their advertisement, and Facebook shows the advertisement to those kinds of people.
You can still use the main Facebook app to message friends. From there, you can view the friend's timeline by clicking the information button in the upper right corner. You don't have to use the stand-alone Messenger app just because it exists.
Subscribers can only see your public posts. You can still control the privacy of your photos, information, etc. by setting the privacy to friends only or friends of friends. You can also choose to not allow anyone to subscribe to you.
But yes, ads are not out of the question in the future.