HTTP/2 is now either supported, or about to be supported by all major browsers.
Most notably, HTTP/2 will be supported by Apple's iOS in version 9, due to launch later this month, which will push HTTP/2 support to hundreds of millions of mobile devices, which are in the best position to benefit from HTTP/2's bandwidth utilization and latency optimizations.
Moreover, shortly after this, browser venders are likely to start to pull support for the now-obsolete pre-standard SPDY protocol, which will make the current SPDY support useless.
See
http://daniel.haxx.se/blog/2015/09/07/http2-115-days-with-the-rfc/
for more details.
At the moment, Wikipedia appears to support SPDY 3.1, but not yet HTTP/2. As far as I can see, many of the major webserver infrastructure projects now either fully support HTTP/2, or have implementations in the works, which in general isn't too difficult, as HTTP/2 is very similar to the last revision of SPDY.
Does anyone know if the WMF engineering team has a schedule for deploying HTTP/2 on its sites, preferably in the near future, and if so, what the progress is toward that goal?
Neil