Lawsuits are sometimes filed for competitive rather than legal reasons. I just feel like Google could cause a huge disruption for traditional employment agencies. I mean if this helps in finding future Google employees then this could work for almost any tech company. Imagine finding an employee for a very specific machine learning project: You could just filter all persons which searched for a certain paper. That also puts Google+ into perspective - you get a better chance at actually identifying that person.

The legal question is if there is a disparate impact.

On a personal level, I really don't like "we hire Python devs if you search on Google for python topics," but that's separate from saying there is a legal challenge here.

You'd have to argue that it is a perpetual monopoly due to the advantage - which I'd say is unlikely.