It's not supported at all on Windows or OS X and the implementations everywhere else are far less tested than TCP. That's a large immediate problem, particularly since you have to update the kernel to fix it, and it also means that many, many intermediaries (home routers, proxies, corporate firewalls, etc.) have never been pushed to support it at all, let alone as well as commonly-used protocols.
The good news is that the semantics are close enough that if the situation improves for both client support and, critically, intermediaries it would be relatively straightforward to migrate to a HTTP/2-over-SCTP hybrid if proved better in some way.
I'm completely aware of the fact that SCTP isn't in the native Windows networking stack, and I'll take your word that it's not in OSX. But as long as we put up all these Frankenstein solutions of handling things up-in-the-stack because firewall admins can't be bothered up upgrade or configure their stuff correctly, we are just not putting out enough pressure that this will get changed!
And even if we now introduce this sad compromise that is HTTP/2, there also will be a lot of proxy/firewall appliances that block HTTP/2, and there will be the equivalent of the government-entity of large corporation that was stuck on IE4/WinXP until 2014 using an outdated web-browser or intranet server.
So, maybe we should try to get incompatible protocols out much earlier and if they turn out to have merit, we could enable them on released products and have Chrome/Firefox put up a nagging reminder: "Your web-experience would be much improved (or: this premium content could be watched at higher resolution, or security to your banking website, or...) if your network infrastructure would support SCTP/IPv6/DNSsec/, please ask your ISP or Administrator".
First, “sad compromise” is a pejorative value judgement and that line of reasoning has just been marketed by people who are appealing to the authority of the legacy OSI model to make “this is new and different and I don't like that” sound more compelling. To make that argument more compelling, someone has to actually do the hard work of analyzing the protocol and pointing out actual, specific engineering problems caused by it which would be fixed by using something like SCTP or why, for example, the predicted sky falling hasn't occurred with in 15 years of TLS not being implemented at the kernel level.
Thus far, the only serious work I've seen shows that something like SCTP or QUIC could possibly be a fair percentage faster on lossy networks. That's something which merits future work, particularly since either would be relatively easy to swap into place for the lower levels of HTTP2 now that the protocol has first-class support for the concepts, but it doesn't seem like a good reason to roll back deployment of a production-ready protocol to wait for everyone to upgrade their kernels first.
> there also will be a lot of proxy/firewall appliances that block HTTP/2
The beauty of reusing HTTPS is that this not the case for most firewalls and since HTTP/2 did not change the semantics, the default behaviour for anyone running an old tampering proxy is not to enjoy the performance benefits but otherwise experience no problems. That seems like a good compromise to me: full backwards compatibility with the cost of non-support being born by the slackers and reusing existing practice means that a much smaller percentage of users are affected.
> nagging reminder: "Your web-experience would be much improved (or: this premium content could be watched at higher resolution, or security to your banking website, or...) if your network infrastructure would support SCTP/IPv6/DNSsec/, please ask your ISP or Administrator".
The problem with this is that most users will just ignore the message and the few who try to escalate it are probably going to be told no because if their ISP/corporate IT was good they'd never have seen the message in the first place.
More seriously, though, there was a time when I had to install MacTCP and others had to install WinSock or Trumpet or whatever it was called. The upgrade was worth it then, and I bet it could be worth it again.
...or just run HTTP over SCTP.
http://en.wikipedia.org/wiki/Stream_Control_Transmission_Pro...