Developer Markus95 has leveraged the PS2 iso functionality of hacked PS4s to run ports of emulators (PGen and QuickNES Retroarch core, respectively). As he mentions himself, these ports are not native PS4 code, but running within the PS2 emulator on the console, and will soon be made obsolete by the expected (hopefully soon?) release of Retroarch for the PS4.
Nonetheless, itís always great to have options.
The issue with using the iso format for your emulator needs is that you have to go through a bit of re-packaging in order to add your roms. As the developer explains: