As easy as SSL is these days, I'm still not sure that it will grab on. With SSLs being as cheap or cheaper than domains these days I don't think it's the holdup with mass adoption. The issue is more complications installing and managing them, and make applications work properly with them.
Great concept, but not sure what it will accomplish what it's intended to.
I think it's less about cost and more about automating the whole thing and making it easier to deal with for people not familiar with installing and maintaining SSL certs. They elude to it here: https://letsencrypt.org/howitworks/ Time will tell I suppose.