Does Windows 8 still implement POSIX?

In the Enterprise Evaluation (essentially, a trial version of Windows 8 Enterprise RTM), SUA is still available through Windows Features, though listed as deprecated:

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Wikipedia states that it is deprecated in Windows 8 and will be removed in Windows 8.1.

WARNING: SUA is deprecated starting with this release and will be completely removed in the next release.

SUA is being removed from Windows kernel. It shows as DEPRECATED which means this is probably the last version of windows which will support it.

Here is a link that suggests so. http://blogs.technet.com/b/sfu/archive/2011/10/03/installing-sua-components-on-windows-8.aspx

SUA is only available in Windows 8 with "premium" client SKUs (meaning Ultimate or Enterprise) or server SKUs (meaning Windows Server 2012). (More info in source.)

SUA is not available in your version of Windows 8 Professional.

You should look for alternatives such as Cygwin or UnxUtils.
A commercial alternative is MKS Toolkit

2016 Windows Subsystem for Linux Update

I don't think this will affect Windows 8, but it might be interesting for newer releases.

In 2016 a new official Linux-like API called "Windows Subsystem for Linux" was announced. It includes Linux system calls, ELF running, parts of the /proc filesystem, Bash, GCC, (TODO likely glibc?), apt-get and more: https://channel9.msdn.com/Events/Build/2016/P488 so I believe that it will allow Windows to run much, if not all, of POSIX. However, it is focused on developers / deployment instead of end users. In particular, there were no plans to allow access to the Windows GUI.