Homebrewing video game consoles has been around for quite a while and many hardwares has been unlocked beyond its normal abilites. In regards to the PlayStation 4, a recent exploit earlier this month allowed for low-level system access on the console for developers.
Through the exploit, hackers were able to introduce Linux support and complete root access via FTP to the system. A homebrew enabler called PS4HEN arrived last week, which means that package files can finally be installed on the PlayStation 4 console.
Other hackers has found a workaround to allow PlayStation 2 games to be playable for the PlayStation 4, and users with the right tools are able to inject their own ISO files to a specially prepared package that installs and runs on compromised consoles.
For the time being, only a selected few from the homebrew community might be fortunate enough to get their hands on the tools needed to do so.