The safe way to clean up WinSxS is with Windows' Deployment Image Servicing and Management (DISM). Running the following in an elevated CMD prompt should theoretically remove some of the excess baggage:
DISM /online /Cleanup-Image /StartComponentCleanup
However, for that task to complete, TrustedInstaller must be running, which is not set up in Windows 8 by default. To run TrustedInstaller, you may need to first enable TelnetServer, then enter
net start TrustedInstaller
After DISM runs successfully (on my PC, I found that DISM worked only when Windows was started in Safe Mode), you may want to disable TelnetServer and stop TrustedInstaller.
After all this folderol, you may find only a modest reduction in the size of WinSxS. In my case, it was reduced from ~10 GB to ~7 GB. sigh.
[It is a great deal easier to use Janitor to clean up old Linux installations and updates, aka "cruff", but Windows is not Linux.]