This is an inherently anti-social feature because it allows asymmetry in the relationship. People want to see what is most relevant to them, not what their friends want to broadcast.
There's currently no way to modulate your volume in social media posts. So "here's a cute photo of my cat" ranks the same as "I really need some help on this". FaceBook amplifies signals that friends like, but this feature allows the poster to amplify as well.
But it uses money, and it's weird to mix money and friend relationships, so... I'm really interested to see how this plays out.
I will be surprised if this feature does anything but lower people's friends counts, as they quickly learn which groups they joined or people they friended are merely funded opportunists.
2. Users probably wouldn't want their friends to know they paid to highlight a post.
I'm not sure how those forces can be reconciled, unless people generally don't care about one [logical OR] the other.
1. Speech for which I am willing to pay to share/announce
2. Speech for which I think Facebook is most appropriate venue
I suspect that overlap is quite small.