I believe the lawsuit is talking about someone using Facebook tools or other means to specifically target subgroups of the population to be able to see a job ad. As in, older candidates would not have even been allowed to know about the job in the first place, regardless of what pipeline a candidate is placed in.

So no, I don't think the properties of a pipeline after a candidate has applied would be related to the lawsuit in the OP, though in principle they could still be relevant for ageism issues.

I am interested in whether companies design candidate pipelines to be generically ageist or discriminatory in other ways, probably ways for which ageism laws are very hard to enforce.

For example, I sincerely view the overwhelming shift to open-plan offices as partly motivated by widespread ageism for the purpose of trying to replace costly older employees with cheaper, more pliable new grads.

I worked in a large education tech company some years ago, and they had a large office in Ohio where most of the HR staff for the whole nationwide HR operations was located. They also had limited IT staff, some regional sales staff, etc., but it was known primarily as "the HR office" because that is where those employees were co-located.

Everyone in the Ohio office had private offices, and many of the staff had been with the company for a long time.

Back in the late 00s, the company completely renovated the whole office building, knocking down walls and reorganizing it so that everyone had to use open-plan shared desk spaces. In one of the end of the year meetings, it was actually revealed that the company spent a ton of money to do this, upwards of $14MM if I remember correctly, and yet they did not have any plan to increase headcount there.

Most of the HR staff were outraged, especially because many aspects of their jobs required private phone calls about confidential HR topics, or calls with job applicants, etc. Even though they needed the ability to make private calls almost every day, the tool they used to do it (private offices) was taken away at expense to the company and replaced with a bank of tiny 1-person phone booth rooms, that you had to compete for every day to book time slots for private calls.

Someone even asked in the company's town hall Q&A why they would do this, and the CEO's response (most of us watched by web stream) was something like, "We are a technology company at heart, and every one of you is an innovator, and innovators love open spaces."

Sure enough, within about 4 years, there had been huge turnover in older HR staff in Ohio, with most positions being replaced by entry level workers, and huge grumblings around the rest of the company that we were not getting the level of support from HR that we needed or had been getting previously.

Really, it was just a restructuring ploy, with a slight bit of ageism (not sure if any part was illegal, but clearly in spirit it was the type of ageism we wish was illegal).

In my mind, a lot of HR processes that are supposed to be fair "because they apply to everyone" are actually just engineered to be processes that would surreptitiously hurt older employees or candidates, even if not outright illegal to do so.