I don’t think that there’s any reason we should expect HTTP/2 to ever be fully adopted, and it’s not really necessary. I am excited to see TLS adopted everywhere and ALPN, SNI available to everyone who needs it, but once you have ALPN you don’t need to adopt HTTP/2. You can just choose to make HTTP/2 available if you think it will help, and in the future you could choose to make HTTP/3 available as well.

As a website operator, the hard part of HTTP/2 was getting TLS certificiates. As an end-user, I'm just happy that popular web pages load faster. And if most of the world still uses HTTP 1.1 I won’t care.

Making a datagram-based protocol available will open up a ton of possibilities for cool realtime apps over HTTP. Currently you’re stuck with WebSockets or WebRTC and for some applications these solutions aren’t good enough.