As the author of an open source webserver, I must say that I'm not really happy with HTTP/2. It adds a lot of extra complexity to the server side of the protocol. And all sorts of ugly and nasty things in HTTP/1 (too much work to go into that right now) have not been fixed.
What I have experienced is that SPDY (and therefor also HTTP/2) will only offer more speed if you are Google or are like Google. Multiplexing doesn't offer that much speed increase as some people would like you to believe. Often, the content of a website is located on multiple systems (pictures, advertisements, etc), which still requires that the browser uses more than one connection, even with HTTP/2. Also, HTTP/1 already allows a browser to send multiple requests without waiting for the response of the previous request. This is called request pipelining, but is turned off by default in most browsers. What I also often see is that a browser makes a first request (often for a CGI script) and the following requests (for the images, JS, CSS, etc) are never made due to browser caching. So, to me HTTP/2 adds a lot of complexity with almost no benefits in return.
Then why do we have HTTP/2? Well, because it's good for Google. They have all the content for their websites on their own servers. Because IETF failed to come up with a HTTP/2 proposal, a commercial company (Google in this case) used that to take control. HTTP/2 is in fact a protocol by Google, for Google.
In my experience, you are far better off with smart caching. With that, you will be able to get far better speed-increase results than HTTP/2 will ever offer. Specially if you use a framework that communicates directly with the webserver about this (like I did with my PHP framework). You will be able to get hundreds to thousands requests per second for a CGI script instead of a few tens of requests. This is a speed increase that HTTP/2 will never offer.
I think this is a failed change to do it right. HTTP is just like SMTP and FTP one of those ancient protocols. In the last 20 years, a lot has changed. HTTP/1 worked fine for those years. But for where the internet is headed, we need something new. Something completely new and not a HTTP/1 patch.