Interesting argument, but the remedy will never be applied from the top (i.e. by means of laws). The reason? Ivy League schools are expensive for a reason -- to reinforce the illusion that being born rich means you're a better, higher-quality person, not part of the riff-raff. Harvard will never accept this.
Also, the declining economic benefit of an advanced degree might by itself reduce the cost of higher education, by means of well-understood economic forces.