Emulation on PC had an exciting year in 2018. There was a lot of development made with both new and old platforms. While there is no current generation emulator available, work has started on a functional PS4 emulator with the first progress update shared recently.
Orbital is a PS4 emulator that is currently in development. It is super early in development and can’t run anything at all, but the first progress update confirmed that it is functioning as intended. It will, of course, need a lot of time before the emulation becomes something viable for PS4 games. It is more of a proof of concept for now.
When it comes to emulation, it is always a gray area on PC. Emulating something that you legally own is fine but most people use it for piracy, which is definitely not okay. What makes emulation interesting is how you are able to break through the limitations of the hardware like resolution or frame rate and run them with better image quality and performance.
You can find out the first progress update on the PS4 emulator Orbital in this video, but be warned, there is no reason to expect this emulator to work at all. It will take years, and that too if there is an interest by the open source developers to work on it. Even though the architecture of PS4 is mostly modern, it still has plenty of customization that will be a hurdle in emulation.