The Chromium team's blog post about this suggests that > 99% of HTTP/2 connections are _already_ negotiated with ALPN [1]. I imagine all of the CDNs and other large providers already use ALPN, so this mostly affects the long tail of small sites. It seems like the claims in the above blog post are overblown.

1 - http://blog.chromium.org/2016/02/transitioning-from-spdy-to-...