Not being on the top-secret list I can’t say whether someone actually did come up with one. But I’m amused that the small and odd band of progressives attempting to defend the filibuster could apparently only muster a case — privatizing social security — in which the filibuster was completely irrelevant. (In addition to Matt and Ezra, see Pierson — the basics of the welfare state proved similarly durable in Westminster systems.)
Of course, even if someone could come up with an isolated example of the filibuster having a progressive impact, it wouldn’t change the fact that the filibuster is a terrible idea in theory that has had horrible effects in practice. The idea that any progressive would defend it is frankly bizarre to me.