This isn't about women posing on Instagram. This is more of a social experiment to change what is trending and how things become "trending".
They said some folks will have private likes, meaning only they can see their likes.
People tend to be followers of what's popular and tend to "like" or give a "reaction" to what everyone else does when it comes to the internet.
Instagram is used by hundreds of millions of people around the world. So any changes that will affect that many people globally is a social experiment.
Things that should be "trending" is news, community issues, social injustices, etc. This might change which issues become a topic of discussion locally, nationally and globally.