Hello,

"In most cases HTTP/2 with NPN in OpenSSL 1.0.1 will work for now.", yes, for now, sadly Google will remove the NPN support in Chrome "soon": "We plan to remove support for SPDY in early 2016, and to also remove support for the TLS extension named NPN in favor of ALPN in Chrome at the same time. Server developers are strongly encouraged to move to HTTP/2 and ALPN.".
Source: http://blog.chromium.org/2015/02/hello-http2-goodbye-spdy.html

Thats why we all have to hurry the migration to ALPN by compiling nginx with OpenSSL 1.0.2 or LibreSSL.

PS : I can't find a good reason for Google to drop support for NPN right now... it feels like last year, when they wanted to drop support of SPDY in Chrome when HTTP/2 was barely standardized and no major web server was HTTP/2 ready.

Best Regards