I'm not sure if this was added to the article after your reply, but the author mentions Hack specifically, along with some caveats about it's adoption, namely that it is currently unkown how widespread Hack will be and how you're basically at Facebook's mercy in regards to the future of the language.
As for adoption, the only stat that I could find was adoption for HHVM[1] (a virtual machine for executing Hack and PHP[2]), but since they list Wikipedia among the HHVM adopters, I'm pretty sure this does not equate to adoption of Hack itself.
As for adoption, the only stat that I could find was adoption for HHVM[1] (a virtual machine for executing Hack and PHP[2]), but since they list Wikipedia among the HHVM adopters, I'm pretty sure this does not equate to adoption of Hack itself.
[1]:https://github.com/facebook/hhvm/wiki/Users [2]:http://hhvm.com/